Resist pattern-forming method, and radiation-sensitive resin composition

ABSTRACT

A resist pattern-forming method includes coating a radiation-sensitive resin composition on a substrate to provide a resist film. The resist film is exposed. The exposed resist film is developed using a developer solution including no less than 80% by mass of an organic solvent. The radiation-sensitive resin composition includes a polymer and a radiation-sensitive acid generator. The polymer has a weight average molecular weight in terms of the polystyrene equivalent of greater than 6,000 and includes a first structural unit that includes an acid-labile group. The polymer includes less than 5 mol % or 0 mol % of a second structural unit that includes a hydroxyl group.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of InternationalApplication No. PCT/JP2011/070197, filed Sep. 5, 2011, which claimspriority to Japanese Patent Application No. 2010-233027, filed Oct. 15,2010 and to Japanese Patent Application No. 2011-066669, filed Mar. 24,2011. The contents of these applications are incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a resist pattern-forming method, and aradiation-sensitive resin composition.

2. Discussion of the Background

Miniaturization of various types of electronic device structures such assemiconductor devices and liquid crystal devices has been accompanied bydemands for miniaturization of resist patterns in lithography processes.Although fine resist patterns having a line width of about 90 nm can beformed using, for example, an ArF excimer laser at present, finer resistpattern formation is required in the future.

To meet the demands described above, as a technique for increasing aresolving power using a preexisting apparatus without increasing stepsby utilizing characteristic features of a chemically amplified typeresist material, a technique in which an organic solvent having polaritylower than that of aqueous alkali solutions is used as a developersolution has been known (see Japanese Unexamined Patent Application,Publication No. 2000-199953). According to such a technique, possibleformation of a fine pattern is exploited since attaining a high opticalcontrast is enabled when an organic solvent is used, contrary to thecase in which a trench pattern or a hole pattern is formed using anaqueous alkali solution as a developer solution, accompanied bydifficulties in forming a fine resist pattern due to lack in an opticalcontrast.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a resistpattern-forming method includes coating a radiation-sensitive resincomposition on a substrate to provide a resist film. The resist film isexposed. The exposed resist film is developed using a developer solutionincluding no less than 80% by mass of an organic solvent. Theradiation-sensitive resin composition includes a polymer and aradiation-sensitive acid generator. The polymer has a weight averagemolecular weight in terms of the polystyrene equivalent of greater than6,000 and includes a first structural unit that includes an acid-labilegroup. The polymer includes less than 5 mol % or 0 mol % of a secondstructural unit that includes a hydroxyl group.

According to another aspect of the present invention, aradiation-sensitive resin composition includes a polymer and aradiation-sensitive acid generator. The polymer has a weight averagemolecular weight in terms of the polystyrene equivalent of greater than6,000 and includes a first structural unit that includes an acid-labilegroup. The polymer includes less than 5 mol % or 0 mol % of a secondstructural unit that includes a hydroxyl group. The radiation-sensitiveresin composition is for use in a resist pattern-forming methodincluding using a developer solution containing no less than 80% by massof an organic solvent.

DESCRIPTION OF THE EMBODIMENTS

According to the embodiment of the present invention made for solvingthe foregoing problems, a resist pattern-forming method includes:

(1) a resist film-forming step of coating a radiation-sensitive resincomposition on a substrate;

(2) an exposure step; and

(3) a development step carried out using a developer solution containingno less than 80% by mass of an organic solvent,

in which the radiation-sensitive resin composition contains:

(A) a polymer which has a weight average molecular weight in terms ofthe polystyrene equivalent of greater than 6,000, and has a structuralunit (I) (may be also referred to as “first structural unit”) thatincludes an acid-labile group, and less than 5 mol % or 0 mol % of astructural unit (may be also referred to as “second structural unit”)that includes a hydroxyl group (hereinafter, may be also referred to as“polymer (A)”); and

(B) a radiation-sensitive acid generator (hereinafter, may be alsoreferred to as “acid generator (B)”).

According to the resist pattern-forming method of the embodiment of thepresent invention, a resist pattern can be formed owing to an action ofan acid generated from the acid generator (B) upon exposure to allow theacid-labile group of the polymer (A) to be dissociated, therebygenerating a polar group such as a carboxyl group to make the polymer(A) hardly soluble in a developer solution containing no less than acertain proportion of an organic solvent. When a polymer having a weightaverage molecular weight in terms of the polystyrene equivalent greaterthan the above certain value, and having a proportion of the structuralunit that includes a hydroxyl group of less than the above value is usedas the polymer (A), the radiation-sensitive resin composition hassuperior resolution, and the resist pattern-forming method enables filmloss of the resist film after the pattern formation to be prevented, andadditionally enables a pattern that is superior in CDU and MEEF to beformed.

Although the reasons for enabling film loss of the resist film to beprevented, and enabling the foregoing lithography characteristics to beimproved by constituting as described above in the resistpattern-forming method have not been necessarily clear, for example thefollowing reason may be envisaged. It is considered that interactionsbetween carboxyl groups, which are produced during exposure, with oneanother, and/or between the carboxyl group and a hydroxyl group in thepolymer (A) account for the film loss, and the interactions are believedto be structurally inhibited as a result of the molecular weight of thepolymer (A) and the proportion of the structural unit that includes ahydroxyl group included falling within the above range, and the like. Inaddition, when the molecular weight of the polymer (A) is greater thanthe certain value, the polymer (A) can be hardly soluble in thedeveloper solution even if a low exposure dose is employed to decreaseproduction of the carboxyl groups, thereby enabling pattern formation.Therefore, interactions between the carboxyl groups with one another canbe consequently decreased, and thus film loss is also believed to beprevented. Furthermore, when the molecular weight of the polymer (A) andthe proportion of the structural unit that includes a hydroxyl groupincluded falls within the above range, it is believed that thedifference resulting from the exposure, i.e., depending on being exposedor unexposed, increases to improve the contrast, whereby a pattern thatis superior in CDU and the like can be obtained. Accordingly, in theresist pattern-forming method in which development is carried out usinga developer solution containing an organic solvent, film loss of theresist film is prevented by using the radiation-sensitive resincomposition containing the polymer that includes the above-specifiedstructure, thereby enabling a resist pattern that is superior in CDU,MEEF to be formed.

The structural unit that includes the acid-labile group is preferablyrepresented by the following formula (1):

wherein, in the formula (1), R represents a hydrogen atom, a fluorineatom, a methyl group or a trifluoromethyl group; and R^(p) represents anacid-labile group represented by the following formula (i):

wherein, in the formula (i), R^(p1) to R^(p3) each independentlyrepresent an alkyl group having 1 to 4 carbon atoms or an alicyclichydrocarbon group having 4 to 9 carbon atoms, or at least two of R^(P1)to R^(P3) taken together represent a divalent alicyclic hydrocarbongroup having 4 to 9 carbon atoms together with the carbon atom to whichR^(P1) to R^(P3) bond.

When the acid-labile group has comparatively few carbon atoms as in theabove structure, a decrease in the molecular weight of the polymer (A)after pattern formation can be inhibited, and as a result, film lossafter pattern formation can be further prevented. In addition, when theacid-labile group has the foregoing properties, substances derived fromthe acid-labile group dissociated scarcely remain in the resist film.Consequently, diffusion of the acid generated from the acid generator(B) is inhibited, whereby a pattern that is superior in CDU, MEEF andthe like can be formed. Also, resolution of the radiation-sensitiveresin composition containing such a polymer (A) is further improved.

It is preferred that: R^(p1), R^(p2) and R^(p3) in the above formula (i)each independently represent an alkyl group having 1 to 4 carbon atoms;or R^(p1) represents an alkyl group having 1 to 4 carbon atoms, andR^(p2) and R^(p3) taken together represent a divalent alicyclichydrocarbon group having 4 to 9 carbon atoms together with the carbonatom to which R^(p2) and R^(p3) bond. When the acid-labile group of thepolymer (A) has the above-specified structure, an alteration of themolecular structure of the polymer (A) resulting from the patternformation can be further suppressed, and the acid-labile group becomesmore likely to be dissociated. Therefore, film loss can be furtherprevented, and formation of a pattern that is superior in CDU, MEEF andthe like is enabled. Moreover, resolution of the radiation-sensitiveresin composition containing such a polymer (A) also can be furtherimproved.

The structural unit (I-1) is preferably included in the structural unit(I) included in the polymer (A) in an amount of no less than 60 mol %and no greater than 95 mol %. When the structural unit (I-1) is includedin the structural unit (I) included in the polymer (A) in an amount ofno less than 60 mol % and no greater than 95 mol %, film loss afterpattern formation of the resist film can be effectively prevented, andadditionally formation of a pattern that is superior in CDU and MEEF isenabled.

The organic solvent is preferably at least one organic solvent selectedfrom the group consisting of an alcohol solvent, an ether solvent, aketone solvent, an amide solvent, an ester solvent and a hydrocarbonsolvent. Since the difference of a solubility of the polymer (A)resulting from the exposure, i.e., depending on being exposed orunexposed, can be increased by using the above-specified organicsolvent, a contrast of the pattern is improved, and formation of apattern further superior in CDU and MEEF is enabled.

The radiation-sensitive resin composition of the embodiment of thepresent invention is a radiation-sensitive resin composition for use ina resist pattern-forming method in which a developer solution containingno less than 80% by mass of an organic solvent is used, theradiation-sensitive resin composition containing: (A) a polymer having aweight average molecular weight in terms of the polystyrene equivalentof greater than 6,000, having a structural unit that includes anacid-labile group, and having less than 5 mol % or 0 mol % of astructural unit that includes a hydroxyl group, and (B) aradiation-sensitive acid generator.

The radiation-sensitive resin composition is superior in the resolution,and according to the radiation-sensitive resin composition, and by usingthe resist pattern-forming method, film loss after pattern formation ofthe resist film can be prevented, and a resist pattern that is superiorin CDU and MEEF can be obtained.

According to the resist pattern-forming method of the embodiment of thepresent invention, film loss after pattern formation of a resist filmcan be prevented, and formation of a resist pattern that is superior inCDU and MEEF is enabled. In addition, the radiation-sensitive resincomposition of the embodiment of the present invention for use in theresist pattern-forming method achieves sufficient resolution. Theembodiments will now be described in detail.

Resist Pattern-Forming Method

An embodiment of the present invention provides a resist pattern-formingmethod including: (1) a resist film-forming step of coating aradiation-sensitive resin composition on a substrate; (2) an exposurestep; and (3) a development step carried out using a developer solutioncontaining no less than 80% by mass of an organic solvent, theradiation-sensitive resin composition containing: (A) a polymer having aweight average molecular weight in terms of the polystyrene equivalentof greater than 6,000, having a structural unit that includes anacid-labile group, and having less than 5 mol % or 0 mol % of astructural unit that includes a hydroxyl group; and (B) aradiation-sensitive acid generator. Hereinafter, each step will bedescribed in detail.

Step (1)

In this step, the radiation-sensitive resin composition of theembodiment of the present invention is coated on a substrate to providea resist film. As the substrate, for example, conventionally well-knownsubstrates such as a silicon wafer and a wafer coated with aluminum canbe used. In addition, organic or inorganic antireflective filmsdisclosed in, for example, Japanese Examined Patent Application,Publication No. H06-12452, Japanese Unexamined Patent Application,Publication No. S59-93448, and the like may be provided on thesubstrate.

A coating method is exemplified by spin-coating, cast coating, rollcoating, and the like. It is to be noted that the film thickness of theresist film provided is typically 0.01 μm to 1 μm, and preferably 0.01μm to 0.5 μm.

After coating the radiation-sensitive resin composition, a solvent inthe coating film may be volatilized as needed by prebaking (PB).According to heating conditions of PB, the temperature may beappropriately selected depending on the formulation of theradiation-sensitive resin composition, and is typically about 30° C. to200° C. and preferably 50° C. to 150° C.

A protective film as disclosed in Japanese Patent ApplicationPublication No. H05-188598 or the like may be provided on the resistlayer so that the resist film is not affected by basic impurities andthe like contained in the environmental atmosphere. Furthermore, inorder to prevent outflow of the acid generating agent and the like fromthe resist layer, a liquid immersion lithography protective film asdisclosed in Japanese Patent Application Publication No. 2005-352384 orthe like may be provided on the resist layer. These techniques may beused in combination.

Step (2)

In this step, the resist film provided in the step (1) is exposed at adesired region by carrying out reduction projection through a maskhaving a specific pattern, and as needed an immersion liquid. Forexample, an isolated trench (iso-trench) pattern can be formed bycarrying out reduced projection exposure at a desired region through amask of an isolated line (iso-line) pattern. Similarly, a hole patterncan be formed by carrying out reduced projection exposure through a dotpattern mask. Also, the exposure may be carried out at least twicedepending on the desired pattern and the mask pattern. When the exposureis carried out at least twice, the exposure is preferably carried outcontinuously. When the exposure is carried out a plurality of times, forexample, first reduced projection exposure is carried out through aline-and-space pattern mask at a desired region, and subsequently secondreduced projection exposure is carried out such that lines cross overlight-exposed sites subjected to the first exposure. The firstlight-exposed sites are preferably orthogonal to the secondlight-exposed sites. Due to being orthogonal with each other, a circularcontact hole pattern can be easily formed at light-unexposed sitessurrounded by light-exposed sites. It is to be noted that examples ofthe immersion liquid for use in the exposure include water, afluorine-containing inert liquid, and the like. It is preferred that theimmersion liquid be transparent to the exposure wavelength, and has atemperature coefficient of the refractive index as small as possible sothat distortion of an optical image projected onto the film isminimized. When an ArF excimer laser (wavelength: 193 nm) is used as theexposure light source, it is preferred to use water from the viewpointof availability and ease of handling, in addition to the viewpointsdescribed above.

A radioactive ray used for the exposure is appropriately selected inaccordance with the type of the acid generator (B), and is exemplifiedby an ultraviolet ray, a far ultraviolet ray, an X-ray, a chargedparticle ray, and the like. Among these, a far ultraviolet ray typifiedby an ArF excimer laser (wavelength: 193 nm) or a KrF excimer laser(wavelength: 248 nm) is preferred, and an ArF excimer laser is morepreferred. The exposure conditions such as an exposure dose areappropriately selected in accordance with the formulation, and type ofadditives etc. of the composition. The resist pattern-forming method ofthe embodiment of the present invention may include a plurality of theexposure steps, and light sources employed in the exposure carried out aplurality of times may be identical or different, but an ArF excimerlaser beam is preferably used in the first exposure step.

In addition, it is preferred that post-exposure baking (PEB) is carriedout after the exposure. When the PEB is carried out, a dissociatereaction of an acid-labile group in the composition can smoothlyproceed. According to heating conditions of PEB, the temperature may betypically 30° C. to 200° C., and preferably 50° C. to 170° C.

Step (3)

In this step, after the exposure in the step (2), development is carriedout using a negative developer solution containing no less than 80% bymass of an organic solvent to form a pattern. The negative developersolution as referred to means a developer solution that selectivelydissolve and remove poorly light-exposed sites and light-unexposedsites. The organic solvent contained in the negative developer solutionis preferably at least one selected from the group consisting of analcohol solvent, an ether solvent, a ketone organic solvent, an amidesolvent, an ester organic solvent and a hydrocarbon solvent.

Examples of the alcohol solvent include:

monohydric alcohol solvents such as methanol, ethanol, n-propanol,iso-propanol, n-butanol, iso-butanol, sec-butanol, tert-butanol,n-pentanol, iso-pentanol, 2-methylbutanol, sec-pentanol, tert-pentanol,3-methoxybutanol, n-hexanol, 2-methylpentanol, sec-hexanol,2-ethylbutanol, sec-heptanol, 3-heptanol, n-octanol, 2-ethylhexanol,sec-octanol, n-nonyl alcohol, 2,6-dimethyl-4-heptanol, n-decanol,sec-undecyl alcohol, trimethylnonyl alcohol, sec-tetradecyl alcohol,sec-heptadecyl alcohol, furfuryl alcohol, phenol, cyclohexanol,methylcyclohexanol, 3,3,5-trimethylcyclohexanol, benzyl alcohol anddiacetone alcohol;

polyhydric alcohol solvents such as ethylene glycol, 1,2-propyleneglycol, 1,3-butylene glycol, 2,4-pentanediol, 2-methyl-2,4-pentanediol,2,5-hexanediol, 2,4-heptanediol, 2-ethyl-1,3-hexanediol, diethyleneglycol, dipropylene glycol, triethylene glycol and tripropylene glycol;

partially etherified polyhydric alcohol solvents such as ethylene glycolmonomethyl ether, ethylene glycol monoethyl ether, ethylene glycolmonopropyl ether, ethylene glycol monobutyl ether, ethylene glycolmonohexyl ether, ethylene glycol monophenyl ether, ethylene glycolmono-2-ethylbutyl ether, diethylene glycol monomethyl ether, diethyleneglycol monoethyl ether, diethylene glycol monopropyl ether, diethyleneglycol monobutyl ether, diethylene glycol monohexyl ether, propyleneglycol monomethyl ether, propylene glycol monoethyl ether, propyleneglycol monopropyl ether, propylene glycol monobutyl ether, dipropyleneglycol monomethyl ether, dipropylene glycol monoethyl ether anddipropylene glycol monopropyl ether, and the like.

Examples of the ether solvent include diethyl ether, dipropyl ether,dibutyl ether, tetrahydrofuran, dioxane, diphenyl ether, methoxybenzene,and the like.

Examples of the ketone solvent include acetone, methyl ethyl ketone,methyl n-propyl ketone, methyl n-butyl ketone, diethyl ketone, methyliso-butyl ketone, methyl n-amyl ketone, ethyl n-butyl ketone, methyln-hexyl ketone, di-iso-butyl ketone, trimethylnonanone, cyclopentanone,cyclohexanone, cycloheptanone, cyclooctanone, methylcyclohexanone,2,4-pentanedione, acetonyl acetone, acetophenone, and the like.

Examples of the amide solvent include N,N′-dimethylimidazolidinone,N-methylformamide, N,N-dimethylformamide, N,N-diethylformamide,acetamide, N-methylacetamide, N,N-dimethylacetamide,N-methylpropionamide, N-methylpyrrolidone, and the like.

Examples of the ester solvent include diethyl carbonate, propylenecarbonate, methyl acetate, ethyl acetate, γ-butyrolactone,γ-valerolactone, n-propyl acetate, iso-propyl acetate, n-butyl acetate,iso-butyl acetate, sec-butyl acetate, n-pentyl acetate, sec-pentylacetate, 3-methoxybutyl acetate, methylpentyl acetate, 2-ethylbutylacetate, 2-ethylhexyl acetate, benzyl acetate, cyclohexyl acetate,methylcyclohexyl acetate, n-nonyl acetate, methyl acetoacetate, ethylacetoacetate, ethylene glycol monomethyl ether acetate, ethylene glycolmonoethyl ether acetate, diethylene glycol monomethyl ether acetate,diethylene glycol monoethyl ether acetate, diethylene glycolmono-n-butyl ether acetate, propylene glycol monomethyl ether acetate,propylene glycol monoethyl ether acetate, propylene glycol monopropylether acetate, propylene glycol monobutyl ether acetate, dipropyleneglycol monomethyl ether acetate, dipropylene glycol monoethyl etheracetate, glycol diacetate, methoxytriglycol acetate, ethyl propionate,n-butyl propionate, iso-amyl propionate, diethyl oxalate, di-n-butyloxalate, methyl lactate, ethyl lactate, n-butyl lactate, n-amyl lactate,diethyl malonate, dimethyl phthalate, diethyl phthalate, and the like.

Examples of the hydrocarbon solvent include:

aliphatic hydrocarbon solvents such as n-pentane, iso-pentane, n-hexane,iso-hexane, n-heptane, iso-heptane, 2,2,4-trimethyl pentane, n-octane,iso-octane, cyclohexane and methylcyclohexane;

aromatic hydrocarbon solvents such as benzene, toluene, xylene,mesitylene, ethylbenzene, trimethylbenzene, methylethylbenzene,n-propylbenzene, i-propylbenzene, diethylbenzene, i-butylbenzene,triethylbenzene, di-i-propylbenzene and n-amylnaphthalene, and the like.

Of these, n-butyl acetate, isopropyl acetate, n-amyl acetate, methylethyl ketone, methyl-n-butyl ketone, and methyl-n-amyl ketone arepreferred. These organic solvents may be used either alone, or incombination of two or more thereof.

The content of the organic solvent in the developer solution is no lessthan 80% by mass. When the content of the organic solvent in thedeveloper solution is no less than 80% by mass, a contrast of thepattern resulting from the exposure, i.e., depending on being exposed orunexposed, can be improved, and consequently, a pattern that is superiorin development characteristics and lithography characteristics can beformed. It is to be noted that examples of components other than theorganic solvent include water, a silicon oil, and the like.

A surfactant may be added to the developer solution in an appropriateamount as needed. As the surfactant, for example, an ionic or nonionicfluorochemical surfactant and/or a silicon surfactant, and the like maybe used.

Examples of the development method include a dipping method thatimmerses the substrate in a container filled with the developer for agiven time, a puddle method that allows the developer to be present onthe surface of the substrate due to surface tension for a given time, aspraying method that sprays the developer onto the surface of thesubstrate, a dynamic dispensing method that applies the developer to thesubstrate that is rotated at a constant speed while scanning with adeveloper application nozzle at a constant speed, and the like.

In the pattern-formation, it is preferred that a step of rinsing theresist film with a rinse agent be carried out after the development inthe step (3). Moreover, also as the rinse agent in the rinsing step, anorganic solvent may be used, whereby scum generated can be efficientlywashed away. The rinse agent is preferably a hydrocarbon solvent, aketone solvent, an ester solvent, an alcohol solvent, an amide solvent,or the like. Of these, an alcohol solvent and an ester solvent arepreferred, and a monovalent alcohol solvent having 6 to 8 carbon atomsis more preferred. The monovalent alcohol having 6 to 8 carbon atoms isexemplified linear, branched or cyclic monovalent alcohols, and examplesthereof include 1-hexanol, 1-heptanol, 1-octanol, 4-methyl-2-pentanol,2-hexanol, 2-heptanol, 2-octanol, 3-hexanol, 3-heptanol, 3-octanol,4-octanol, benzyl alcohol, and the like. Of these, 1-hexanol, 2-hexanol,2-heptanol, and 4-methyl-2-pentanol are preferred.

Each component of the rinse agent may be used either alone, or incombination of two or more thereof. The moisture content in the rinseagent is preferably no greater than 10% by mass, more preferably nogreater than 5% by mass, and still more preferably no greater than 3% bymass. When the moisture content is no greater than 10% by mass,favorable development characteristics can be attained. It is to be notedthat a surfactant may be added to a rinse agent described later.

Examples of the rinsing method include a spinning method that appliesthe rinse agent to the substrate that is rotated at a constant speed, adipping method that immerses the substrate in a container filled withthe rinse agent for a given time, a spraying method that sprays therinse agent onto the surface of the substrate, and the like.

Radiation-Sensitive Resin Composition

The radiation-sensitive resin composition for use in the embodiment ofthe present invention contains (A) a polymer, and (B) an acid generator,and may further contain optional components within a range not leadingto impairment of the effects of the embodiment of the present invention.Hereinafter, each component will be described in detail.

(A) Polymer

The polymer (A) has a weight average molecular weight in terms of thepolystyrene equivalent of greater than 6,000, having a structural unit(I) that includes an acid-labile group, and having less than 5 mol % or0 mol % of a structural unit that includes a hydroxyl group. Accordingto the resist pattern-forming method, the film loss after patternformation of the resultant resist film can be prevented, and formationof a pattern that is superior in CDU and the like is enabled when thepolymer (A) has the above-specified properties.

Although the reasons for enabling film loss after pattern formation ofthe resist film to be prevented, and enabling the foregoing lithographycharacteristics of the radiation-sensitive resin composition containingthe polymer (A) to be improved, due to the polymer (A) having thecharacteristics described above in the resist pattern-forming methodhave not been necessarily clear. However, it is considered, for example,that interactions between carboxyl groups, which are produced duringexposure, with one another, and/or between the carboxyl group and ahydroxyl group in the polymer (A) may be one cause of the film loss, andthe interactions are believed to be structurally inhibited as a resultof the molecular weight of the polymer (A) and the proportion of thestructural unit that includes a hydroxyl group included falling withinthe above range, and the like. Also, with regard to lithographyperformances evaluated in accordance with CDU, etc., as an index, whenthe molecular weight of the polymer (A) and the proportion of thestructural unit that includes a hydroxyl group included falls within theabove range, it is believed that the difference resulting from theexposure, i.e., depending on being exposed or unexposed, increases toimprove the contrast, in addition to achieving the effect of preventingthe film loss.

On the other hand, since the polymer (A) has a molecular weight greaterthan a predetermined value, and low solubility in a developer solutioncontaining an organic solvent, a pattern can be formed at a lowerexposure dose. Thus, the amount of the carboxyl group generated inpattern formation can be further reduced, and interactions betweencarboxyl groups can be decreased, whereby the film loss can be furtherprevented.

The polymer (A) essentially has a weight average molecular weight interms of the polystyrene equivalent (hereinafter, may be also referredto as “Mw”) of greater than 6,000. When the Mw of the polymer (A) isgreater than 6,000, film loss after pattern formation of the resultantresist film can be prevented, along with improvement of lithographycharacteristics such as CDU, as a synergistic effect with the proportionof the structural unit that includes a hydroxyl group included beingless than the predetermined value as described later. The Mw of thepolymer (A) is typically greater than 6,000 and no greater than 100,000,preferably greater than 6,000 and no greater than 30,000, and morepreferably greater than 8,000 and no greater than 20,000. When the Mw ofthe polymer (A) is no greater than 6,000, marked film loss of theresultant resist pattern, and reduction of etching resistance occur, aswell as remarkable deterioration of lithography characteristics such asCDU tend to occur. Furthermore, when the Mw is greater than 100,000, adifference of solubility of the polymer (A) resulting from the exposure,i.e., depending on being exposed or unexposed becomes so small thatlithography characteristic may be deteriorated.

The number average molecular weight in terms of the polystyreneequivalent (hereinafter, may be also referred to as “Mn”) of the polymer(A) is 2,000 to 60,000, preferably 3,000 to 40,000, and particularlypreferably 4,000 to 20,000.

The ratio (Mw/Mn) of the weight average molecular weight (Mw) to thenumber average molecular weight (Mn) of the polymer (A) is typically 1to 3, and preferably 1 to 2. It is to be noted that values of the Mw andthe Mn may be determined by measurement on gel permeation chromatography(GPC) using polystyrene as a standard.

The content of the low molecular weight components in the polymer (A) ispreferably no greater than 0.15% by mass, more preferably no greaterthan 0.07% by mass, and still more preferably no greater than 0.04% bymass. When the content of the low molecular weight components fallswithin the above range, interactions between carboxyl groups, etc.,generated after pattern formation of the resultant resist film are lesslikely to occur, whereby the film loss can be further prevented. It isto be noted that the “low molecular weight components” mean componentshaving a molecular weight of less than 1,000, and the content thereofmay be determined by high performance liquid chromatography (HPLC).

Structural Unit (I) that Includes Acid-Labile Group

The polymer (A) has a structural unit that includes an acid-labile group(hereinafter, may be also referred to as “structural unit (I)”). Theterm “acid-labile group” as referred to herein means a group thatsubstitutes for a hydrogen atom in a polar functional group such as acarboxyl group, and is dissociated by an action of an acid generatedfrom the acid generator (B) upon exposure. Since the polymer (A) has thestructural unit that includes an acid-labile group, the number of thepolar functional groups such as a carboxyl group increases uponexposure, leading to an increase in polarity as a whole of the polymer,and thus the solubility in a developer solution containing an organicsolvent decreases, whereby a favorable resist pattern can be formed.

The structural unit (I) is not particularly limited as long as anacid-labile group is included in the structural unit. The number of theacid-labile group in the structural unit (I) may be one, or two or more.In addition, the position of the acid-labile group in the structuralunit (I) is also not particularly limited as long as it substitutes fora hydrogen atom in the polar functional group. The acid-labile group isnot particularly limited as long as it has the acid-dissociatingproperty described above.

The acid-labile group preferably has an alicyclic hydrocarbon group.When the acid-labile group has an alicyclic hydrocarbon group, theacid-labile group is likely to be dissociated, and as a result,lithography characteristics of the resultant resist film are furtherimproved.

Specific example of preferred structural unit (I) is the structural unitrepresented by the above formula (1) (hereinafter, may be also referredto as “structural unit (I-1)”).

Structural Unit (I-1)

The structural unit (I-1) is represented by the above formula (1). Sincethe number of carbon atoms constituting the acid-labile group of thestructural unit (I-1) is relatively small, a decrease in the molecularweight of the polymer (A) after pattern formation can be suppressed, andas a result, film loss after pattern formation can be further prevented.In addition, for similar reasons to those described above, substancesderived from the acid-labile group dissociated scarcely remain in theresist film, and consequently, diffusion of the acid generated from theacid generator (B) is inhibited, whereby the lithography characteristicssuch as CDU are further improved. In addition, since a monomer thatgives the structural unit (I-1) is superior in copolymerizability, thecontent of the acid-labile group in the polymer (A) can be convenientlyadjusted to a desired value. Furthermore, since the monomer that givesthe structural unit (I-1) can be readily synthesized, the acid-labilegroup of the polymer (A) having a desired structure can be convenientlyprovided.

In the above formula (1), R represents a hydrogen atom, a fluorine atom,a methyl group or a trifluoromethyl group; and R^(p) is represented bythe above formula (i). In the above formula (i), R^(p1) to R^(p3) eachindependently represent an alkyl group having 1 to 4 carbon atoms or analicyclic hydrocarbon group having 4 to 9 carbon atoms, or at least twoof R^(P1) to R^(P3) taken together represent a divalent alicyclichydrocarbon group having 4 to 9 carbon atoms together with the carbonatom to which the at least two of R^(P1) to R^(P3) bond.

Examples of the alkyl group having 1 to 4 carbon atoms represented byR^(p1) to R^(p3) in the above formula (i) include a methyl group, anethyl group, a n-propyl group, an i-propyl group, a n-butyl group, a2-methylpropyl group, a 1-methylpropyl group, a t-butyl group, and thelike.

Examples of the monovalent alicyclic hydrocarbon group having 4 to 9carbon atoms represented by R^(p1) to R^(p3) in the above formula (i)include:

polycyclic alicyclic groups having a bridged skeleton such as anorbornane skeleton;

monocyclic alicyclic groups having a cycloalkane skeleton such ascyclopentane and cyclohexane;

hydrocarbon groups having any of these monocyclic or polycyclicalicyclic groups; and the like. Moreover, these groups are unsubstitutedor substituted with, for example, at least one linear, branched orcyclic alkyl group having 1 to 10 carbon atoms.

The divalent alicyclic hydrocarbon group taken together represented byat least two of R^(P1) to R^(P3) together with the carbon atom to whichthe at least two of R^(P1) to R^(P3) bond in the above formula (i) isexemplified by a group derived by removing one hydrogen atom from themonovalent group exemplified as the monovalent alicyclic hydrocarbongroup having 4 to 9 carbon atoms represented by R^(p1) to R^(p3) in theabove formula (i).

Among combinations of the R^(p1) to R^(p30), it is further preferredthat in the above formula (i): R^(p1), R^(p2) and R^(p3) represent analkyl group having 1 to 4 carbon atoms; or R^(p1) represents an alkylgroup having 1 to 4 carbon atoms, and R^(p2) and R^(p3) taken togetherrepresent an alicyclic hydrocarbon group such as a divalent cycloalkaneskeleton having 4 to 9 carbon atoms together with the carbon atom towhich R^(p2) and R^(p3) bond.

When the acid-labile group that includes R^(p1) to R^(p3) has theaforementioned structure, an alteration of the molecular structure ofthe polymer (A) after the pattern formation can be suppressed, and theacid-labile group is more likely to be dissociated; therefore, the filmloss can be further prevented, and lithography characteristics evaluatedin accordance with MEEF, etc., as an index, can be further improved.

Examples of preferred structural unit (I-1) include structural unitsrepresented by the following formulae (1-1) to (1-4).

In the formulae (1-1) to (1-4), R is as defined in the above formula(1); R^(p1), R^(p2) and R^(p3) are as defined in the above formula (i);and n_(p) is an integer of 1 to 4.

Specific examples of the structural units represented by the aboveformulae (1) or (1-1) to (1-4) include structural units represented bythe following formulae.

In the formulae, R is as defined in the above formula (1).

Among these specific examples of the structural units represented by theabove formula (1) and the above formulae (1-1) to (1-4), structuralunits having as an acid-labile group a norbornyl group or a cycloalkylgroup substituted with an alkyl group at position 1 are preferred, andof these, structural units having as an acid-labile group a cyclopentylgroup or a cyclohexyl group substituted with an alkyl group at position1, and a t-butyl group are more preferred.

Structural Unit (I-2)

The structural unit (I) may have in addition to the structural unit(I-1), for example, a structural unit represented by the followingformula (2) (hereinafter, may be also referred to as “structural unit(I-2)”) for the purpose of adjusting the resolution, solubility atlight-unexposed sites, and the like.

In the above formula (2), R^(b1) represents a hydrogen atom or a methylgroup; and R^(b2) represents a group that includes a monovalentalicyclic group having 10 to 20 carbon atoms. In the alicyclic group, apart or all of hydrogen atoms are unsubstituted or substituted with analkyl group having 1 to 4 carbon atoms.

The monovalent alicyclic group having 10 to 20 carbon atoms representedby R^(b2) is exemplified by bridged alicyclic groups such as atricyclodecanyl group, a tetracyclododecanyl group and an adamantylgroup, and the like.

Examples of the structural unit (I-2) include structural unitsrepresented by the following formulae, and the like.

In the above formulae, R^(b1) is as defined in the above formula (2).

The lower limit of the proportion of the structural unit (I) included inthe polymer (A) is preferably 5 mol %, more preferably 10 mol %, stillmore preferably 20 mol %, particularly preferably 30 mol %, and mostpreferably 40 mol %. On the other hand, the upper limit of theproportion of the structural unit (I) included is preferably 90 mol %,more preferably 80 mol %, still more preferably 70 mol %, andparticularly preferably 60 mol %. When the proportion of the structuralunit (I) included is less than the lower limit, sensitivity of theradiation-sensitive resin composition obtained may be deteriorated. Tothe contrary, when the proportion of the structural unit (I) included isless than the upper limit, pattern formability may be deteriorated. Thepolymer (A) may have one type, or two or more types of the structuralunit (I).

The proportion of the structural unit (I-1) in the structural unit (I)in the polymer (A) is typically 60 to 95 mol %, preferably 65 to 95 mol%, and more preferably 70 to 90 mol %. When the proportion of thestructural unit (I-1) falls within the above range, favorable solubilityof the resultant resist film in an organic solvent is attained, and thuspattern formation with high resolution and prevention of film loss afterpattern formation can be both achieved.

Structural Unit that Includes Hydroxyl Group (II)

The polymer (A) may have a structural unit that includes a hydroxylgroup (hereinafter, may be also referred to as “structural unit (II)”),and the content is essentially less than 5 mol %. When the content ofthe structural unit (II) is less than 5 mol % or 0 mol %, film lossafter pattern formation of the resultant resist film can be prevented bya synergistic effect in combination with the effect achieved by theweight average molecular weight in terms of styrene of the polymer (A)exceeding the predetermined value. Also, in addition to the preventionof film loss, an alteration of the polarity of the polymer (A) can befurther enhanced after dissociation of the acid-labile group of thepolymer (A); therefore, lithography characteristics such as CDU can beconsequently improved. The content of the structural unit (II) in thepolymer (A) is preferably no greater than 4 mol %, more preferably 2 mol%, and particularly preferably 0 mol %, thus in other words, the polymer(A) preferably has no structural unit (II).

The structural unit (II) is not particularly limited as long as ahydroxyl group is included in its structural unit. The number of thehydroxyl group in the structural unit (II) may be one, or two or more,and in light of enhancement of an alteration of the polarity of thepolymer (A) after pattern formation, the number of the hydroxyl group ispreferably the smaller, more preferably no greater than 2, andparticularly preferably 1. Also, the position of the hydroxyl group inthe structural unit (II) is not particularly limited. Specific examplesof the structural unit (II) include structural units represented by thefollowing formulae.

In the above formula, R¹ represents a hydrogen atom, a fluorine atom, amethyl group or a trifluoromethyl group.

Structural Unit (III) that Includes Lactone-Containing Group or CyclicCarbonate-Containing Group

The polymer (A) preferably has a structural unit (hereinafter, may bealso referred to as “structural unit (III)”) that includes alactone-containing group or a cyclic carbonate-containing group.Adhesiveness of the resist film to a substrate can be improved when thepolymer (A) has the structural unit (III). In addition, solubility ofthe resist film in a developer solution can be improved. The“lactone-containing group” as herein referred to indicates a cyclicgroup having one ring that includes a bond represented by —O—C(O)—(i.e., lactone ring). Further, the “cyclic carbonate-containing group”indicates a cyclic group having one ring that includes a bondrepresented by —O—C(O)—O— (i.e., cyclic carbonate ring). The lactonering or the cyclic carbonate ring is counted as a first ring, and whenonly the lactone ring or the cyclic carbonate ring is included, thegroup is referred to as a “monocyclic group”, whereas when other ringstructure is further included, the group is referred to as a “polycyclicgroup”, irrespective of its structure.

Examples of the structural unit (III) include structural unitsrepresented by the following formulae, and the like.

In the above formulae, R^(L1) represents a hydrogen atom, a fluorineatom, a methyl group or a trifluoromethyl group.

It is preferred that the structural unit (III) has no polar group otherthan a lactone group, a cyclic carbonate group and an ester group, orhas no functional group that generates a polar group by an action of theacid generator (B) upon exposure. The absence of the polar group and/orthe functional group that generates a polar group can lead to anincrease of a difference resulting from the exposure, i.e., depending onbeing exposed or unexposed the difference of polarity of the polymer(A); therefore, lithography characteristics such as CDU can be furtherimproved. Examples of the polar group include a cyano group, an alkoxygroup, an amino group, a dialkylamino group, an amide group, and thelike. In addition, examples of the functional group that generates apolar group by an action of the acid generator (B) include an acetalgroup, a ketal group, a carbamate group, and the like.

Examples of the monomer that yields that structural unit (III) includemonomers represented by the following formula (L-1), and the like.

In the above formula (L-1), R^(L1) represents a hydrogen atom, afluorine atom, a methyl group or a trifluoromethyl group; R^(L2)represents a single bond or a divalent linking group; and R^(L3)represents a monovalent organic group having a lactone structure or acyclic carbonate structure.

The divalent linking group represented by R^(L2) is exemplified by adivalent linear or branched hydrocarbon group having 1 to 20 carbonatoms, and the like.

Examples of the monovalent organic group having a lactone structurerepresented by R^(L3) include groups represented by the followingformulae (L3-1) to (L3-6), and the like. Examples of the monovalentorganic group having a cyclic carbonate structure represented by R^(L3)include groups represented by the following formulae (L3-7) and (L3-8),and the like.

In the formulae (L3-1) and (L3-4), R^(Lc1) represents an oxygen atom ora methylene group.

In the formula (L3-3), R^(Lc2) represents a hydrogen atom or an alkylgroup having 1 to 4 carbon atoms.

In the formulae (L3-1) and (L3-2), n_(Lc1) is 0 or 1.

In the formula (L3-3), n_(Lc2) is an integer of 0 to 3.

In the formula (L3-7), n_(c1) is an integer of 0 to 2.

In the formula (L3-8), n_(c2) to n_(c5) are each independently aninteger of 0 to 2, and “*” indicates an atomic bonding that links toR^(L2) in the above formula (L-1).

-   It is to be noted that groups represented by the formulae (L3-1) to    (L3-8) may have a substituent.

Preferable monomers that give the structural unit (III) include, forexample, monomers described in paragraph [0043] of PCT InternationalPublication No. 2007/116664, and the like.

In the polymer (A), the proportion of the structural unit (III) includedis preferably 30 mol % to 60 mol %. When the content of the structuralunit (III) in the polymer (A) falls within the above range, adhesivenessof the resist pattern obtained can be improved.

Other Structural Unit

The polymer (A) may have a structural unit that includes an alicyclicstructure (excluding those included in the structural unit (I)), etc.,in order to further improve the etching resistance.

The structural unit that includes an alicyclic structure is exemplifiedby a structural unit represented by the following formula (4), and thelike.

In the above formula (4), R⁶ represents a hydrogen atom, a fluorineatom, a methyl group or a trifluoromethyl group; and X² represents amonovalent alicyclic hydrocarbon group having 4 to 20 carbon atoms.

The monovalent alicyclic hydrocarbon group having 4 to 20 carbon atomsrepresented by X² is exemplified by a group derived by removing onehydrogen atom from cyclobutane, cyclopentane, cyclohexane,bicyclo[2.2.1]heptane, bicyclo[2.2.2]octane,tricyclo[5.2.1.0^(2,6)]decane,tetracyclo[6.2.1.1^(3,6.)0^(2,7)]dodecane, tricyclo[3.3.1.1^(3,7)]decaneor the like. These monovalent alicyclic hydrocarbon groups having 4 to20 carbon atoms may have a substituent. Examples of the substituentinclude linear, branched or cyclic alkyl group having 1 to 4 carbonatoms such as a methyl group, an ethyl group, a n-propyl group, ani-propyl group, a n-butyl group, a 2-methylpropyl group, a1-methylpropyl group and a t-butyl group, a hydroxyl group, a cyanogroup, a hydroxyalkyl group having 1 to 10 carbon atoms, a carboxylgroup, an oxygen atom, and the like.

Examples of the monomer that gives the structural unit that includes analicyclic structure include (meth)acrylic acid-bicyclo[2.2.1]hept-2-ylester, (meth)acrylic acid-bicyclo[2.2.2]oct-2-yl ester, (meth)acrylicacid-tricyclo[5.2.1.0^(2,6)]dec-7-yl ester, (meth)acrylicacid-tricyclo[3.3.1.1^(3,7)]dec-1-yl ester, (meth)acrylicacid-tricyclo[3.3.1.1^(3,7)]dec-2-yl ester, and the like.

In the polymer (A), each only one type, or two or more types of thestructural unit (I), the structural unit (II), the structural unit (III)and the other structural unit may be included. It is to be noted thatthe polymer (A) preferably does not include a structural unit having anaromatic group. When the polymer (A) includes a structural unit havingan aromatic group, a decrease in sensitivity may be caused particularlyin the case in which an ArF light source is used, and the shape may bedeteriorated further in the case in which development is carried outusing a negative developer solution.

Synthesis Method of Polymer (A)

The polymer (A) may be prepared, for example, by polymerizing themonomer that corresponds to each predetermined structural unit in anappropriate solvent using a radical polymerization initiator.

Examples of the radical polymerization initiator include: azo radicalinitiators such as azobisisobutyronitrile (AIBN),2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile),2,2′-azobis(2-cyclopropylpropionitrile),2,2′-azobis(2,4-dimethylvaleronitrile) and dimethyl2,2′-azobisisobutyrate; peroxide radical initiators such asbenzoylperoxide, t-butylhydroperoxide and cumenehydroperoxide, and thelike. Among these, AIBN and dimethyl 2,2′-azobisisobutyrate arepreferred. These radical initiators may be used either alone, or as amixture of two or more thereof.

Examples of solvent for use in the polymerization include:

alkanes such as n-pentane, n-hexane, n-heptane, n-octane, n-nonane andn-decane;

cycloalkanes such as cyclohexane, cycloheptane, cyclooctane, decalin andnorbornane;

aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene andcumene;

halogenated hydrocarbons such as chlorobutanes, bromohexanes,dichloroethanes, hexamethylene dibromide and chlorobenzene;

saturated carboxylate esters such as ethyl acetate, n-butyl acetate,i-butyl acetate and methyl propionate;

ketones such as acetone, 2-butanone, 4-methyl-2-pentanone and2-heptanone;

ethers such as tetrahydrofuran, dimethoxyethanes and diethoxyethanes;

alcohols such as methanol, ethanol, 1-propanol, 2-propanol and4-methyl-2-pentanol; and the like. These solvents may be used eitheralone, or in combination of two or more thereof.

The reaction temperature in the polymerization is typically 40° C. to150° C., and preferably 50° C. to 120° C. The reaction time is typically1 hour to 48 hrs, and preferably 1 hour to 24 hrs.

(B) Acid Generator

The acid generator (B) generates an acid upon exposure, and the acidallows an acid-labile group present in the polymer (A) to bedissociated, thereby generating a polar group such as a carboxyl group.As a result, the polymer (A) becomes hardly soluble in developersolutions containing an organic solvent. The mode of incorporation ofthe acid generator (B) into the radiation-sensitive resin compositionmay be a form of being incorporated as a compound as described below(hereinafter, may be appropriately referred to as “acid generating agent(B)”), a form of being incorporated as a part of a polymer, or acombination of these two forms.

The acid generating agent (B) is exemplified by an onium salt compound,a sulfonimide compound, a halogen-containing compound, a diazo ketonecompound, and the like. Of these acid generating agents (B), an oniumsalt compound is preferred.

Examples of the onium salt compound include sulfonium salts (includingtetrahydrothiophenium salts), iodonium salts, phosphonium salts,diazonium salts, pyridinium salts, and the like.

Examples of the sulfonium salt include triphenylsulfoniumtrifluoromethanesulfonate, triphenylsulfoniumnonafluoro-n-butanesulfonate, triphenylsulfoniumperfluoro-n-octanesulfonate, triphenylsulfonium2-bicyclo[2.2.1]hept-2-yl-1,1,2,2-tetrafluoroethanesulfonate,triphenylsulfonium camphorsulfonate, 4-cyclohexylphenyldiphenylsulfoniumtrifluoromethanesulfonate, 4-cyclohexylphenyldiphenylsulfoniumnonafluoro-n-butanesulfonate, 4-cyclohexylphenyldiphenylsulfoniumperfluoro-n-octanesulfonate, 4-cyclohexylphenyldiphenylsulfonium2-bicyclo[2.2.1]hept-2-yl-1,1,2,2-tetrafluoroethanesulfonate,4-cyclohexylphenyldiphenylsulfonium camphorsulfonate,4-methanesulfonylphenyldiphenylsulfonium trifluoromethanesulfonate,4-methanesulfonylphenyldiphenylsulfonium nonafluoro-n-butanesulfonate,4-methanesulfonylphenyldiphenylsulfonium perfluoro-n-octanesulfonate,4-methanesulfonylphenyldiphenylsulfonium2-bicyclo[2.2.1]hept-2-yl-1,1,2,2-tetrafluoroethanesulfonate,4-methanesulfonylphenyldiphenylsulfonium camphorsulfonate,2-adamantyl-1,1-difluoroethane-1-sulfonate, triphenylphosphonium1,1,2,2-tetrafluoro-6-(1-adamantanecarbonyloxy)-hexane-1-sulfonate, andthe like. Among these, triphenylsulfonium trifluoromethanesulfonate,triphenylsulfonium nonafluoro-n-butanesulfonate,2-adamantyl-1,1-difluoroethane-1-sulfonate, and triphenylphosphonium1,1,2,2-tetrafluoro-6-(1-adamantanecarbonyloxy)-hexane-1-sulfonate arepreferred.

Examples of the tetrahydrothiophenium salt include1-(4-n-butoxynaphthalen-1-yl)tetrahydrothiopheniumtrifluoromethanesulfonate,1-(4-n-butoxynaphthalen-1-yl)tetrahydrothiopheniumnonafluoro-n-butanesulfonate,1-(4-n-butoxynaphthalen-1-yl)tetrahydrothiopheniumperfluoro-n-octanesulfonate,1-(4-n-butoxynaphthalen-1-yl)tetrahydrothiophenium2-bicyclo[2.2.1]hept-2-yl-1,1,2,2-tetrafluoroethanesulfonate,1-(4-n-butoxynaphthalen-1-yl)tetrahydrothiophenium camphorsulfonate,1-(6-n-butoxynaphthalen-2-yl)tetrahydrothiopheniumtrifluoromethanesulfonate,1-(6-n-butoxynaphthalen-2-yl)tetrahydrothiopheniumnonafluoro-n-butanesulfonate,1-(6-n-butoxynaphthalen-2-yl)tetrahydrothiopheniumperfluoro-n-octanesulfonate,1-(6-n-butoxynaphthalen-2-yl)tetrahydrothiophenium2-bicyclo[2.2.1]hept-2-yl-1,1,2,2-tetrafluoroethanesulfonate,1-(6-n-butoxynaphthalen-2-yl)tetrahydrothiophenium camphorsulfonate,1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiopheniumtrifluoromethanesulfonate,1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiopheniumnonafluoro-n-butanesulfonate,1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiopheniumperfluoro-n-octanesulfonate,1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiophenium2-bicyclo[2.2.1]hept-2-yl-1,1,2,2-tetrafluoroethanesulfonate,1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiophenium camphorsulfonate,and the like. Among these tetrahydrothiophenium salts,1-(4-n-butoxynaphthalen-1-yl) tetrahydrothiopheniumnonafluoro-n-butanesulfonate,1-(4-n-butoxynaphthalen-1-yl)tetrahydrothiopheniumperfluoro-n-octanesulfonate and1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiopheniumnonafluoro-n-butanesulfonate are preferred.

Examples of the iodonium salt include diphenyliodoniumtrifluoromethanesulfonate, diphenyliodoniumnonafluoro-n-butanesulfonate, diphenyliodoniumperfluoro-n-octanesulfonate, diphenyliodonium2-bicyclo[2.2.1]hept-2-yl-1,1,2,2-tetrafluoroethanesulfonate,diphenyliodonium camphorsulfonate, bis(4-t-butylphenyl)iodoniumtrifluoromethanesulfonate, bis(4-t-butylphenyl)iodoniumnonafluoro-n-butanesulfonate, bis(4-t-butylphenyl)iodoniumperfluoro-n-octanesulfonate, bis(4-t-butylphenyl)iodonium2-bicyclo[2.2.1]hept-2-yl-1,1,2,2-tetrafluoroethanesulfonate,bis(4-t-butylphenyl)iodonium camphorsulfonate, and the like. Among theseiodonium salts, bis(4-t-butylphenyl)iodoniumnonafluoro-n-butanesulfonate is preferred.

Examples of the sulfonimide compound includeN-(trifluoromethanesulfonyloxy)bicyclo[2.2.1]hept-5-ene-2,3-dicarboxyimide,N-(nonafluoro-n-butanesulfonyloxy)bicyclo[2.2.1]hept-5-ene-2,3-dicarboxyimide,N-(perfluoro-n-octanesulfonyloxy)bicyclo[2.2.1]hept-5-ene-2,3-dicarboxyimide,N-(2-bicyclo[2.2.1]hept-2-yl-1,1,2,2-tetrafluoroethanesulfonyloxy)bicyclo[2.2.1]hept-5-ene-2,3-dicarboxyimide,N-(2-(3-tetracyclo[4.4.0.1^(2,5.)1^(7,10)]dodecanyl)-1,1-difluoroethanesulfonyloxy)bicyclo[2.2.1]hept-5-ene-2,3-dicarboxyimide,N-(camphorsulfonyloxy)bicyclo[2.2.1]hept-5-ene-2,3-dicarboxyimide, andthe like. Among these sulfonimide compounds,N-(trifluoromethanesulfonyloxy)bicyclo[2.2.1]hept-5-ene-2,3-dicarboxyimideis preferred.

These acid generators (B) may be used either alone, or in combination oftwo or more thereof. The amount of the acid generator (B) employed inthe case of the acid generator (B) being the acid generating agent istypically no less than 0.1 parts by mass and no greater than 30 parts bymass, and preferably no less than 0.5 parts by mass and no greater than20 parts by mass with respect to 100 parts by mass of the polymer (A) inview of ensuring the sensitivity and developability for use as a resist.In this case, when the amount of the acid generating agent (B) employedis less than 0.1 parts by mass, the sensitivity and developability tendto be deteriorated, whereas the amount of the acid generating agent (B)exceeding 30 parts by mass is likely to result in reduction of radiationtransmittance, and to render the formation of the desired resistpatterns difficult.

Optional Components

In addition to the polymer (A) and the acid generator (B), theradiation-sensitive resin composition may contain a fluorineatom-containing polymer, an acid diffusion controller, a solvent, asurfactant, an alicyclic skeleton-containing compound, a sensitizingagent and the like as optional components within a range not leading toimpairment of the effects of the present invention.

Fluorine Atom-Containing Polymer

The radiation-sensitive resin composition may contain a fluorineatom-containing polymer (excluding the polymer (A)). When theradiation-sensitive resin composition contains the fluorineatom-containing polymer, the polymer tends to be unevenly distributedaround the surface layer of the resist film in forming the resist film,due to an oil repellent feature of the fluorine atom-containing polymer.Thus, elution of the acid generating agent, the acid diffusion controlagent, etc., in the film into the liquid immersion medium during liquidimmersion lithography can be inhibited. In addition, owing to a waterrepellent feature of the fluorine atom-containing polymer, an advancingcontact angle of a liquid immersion medium on a resist film can becontrolled to fall within a desired range, whereby formation of bubbledefects can be suppressed. Furthermore, a higher receding contact angleof a liquid immersion medium on a resist film can be attained, therebyconsequently enabling exposure by high-speed scanning without remainingwater droplets. The radiation-sensitive resin composition thuscontaining the fluorine atom-containing polymer enables a resist film tobe formed which is suitable for a liquid immersion lithography process.

The fluorine atom-containing polymer is not particularly limited as longas it contains a fluorine atom, and can be generally prepared bypolymerizing one or more types of monomers that include a fluorine atomin the structure thereof. The monomers that include a fluorine atom inthe structure thereof are exemplified by a monomer that includes afluorine atom in its main chain, a monomer that includes a fluorine atomin its side chain, and a monomer that includes a fluorine atom in itsmain chain and side chain.

Examples of the monomer that includes a fluorine atom in its main chaininclude α-fluoroacrylate compounds, α-trifluoromethyl acrylatecompounds, β-fluoroacrylate compounds, β-trifluoromethyl acrylatecompounds, α,β-fluoroacrylate compounds, α,β-trifluoromethyl acrylatecompounds, compounds derived by substituting hydrogen of one or moretypes of vinyl moieties by a fluorine atom, a trifluoromethyl group,etc., and the like.

Examples of the monomer that includes a fluorine atom in its side chaininclude compounds in which an alicyclic olefin compound such asnorbornene has a fluorine atom, a fluoroalkyl group and/or a derivativethereof as a side chain, ester compounds produced from acrylic acid ormethacrylic acid with fluoroalkyl alcohol and/or a derivative thereof,olefins having a fluorine atom, a fluoroalkyl group and/or a derivativethereof as one or more types of side chain (a site excluding a doublebond), and the like.

Examples of the monomer that includes a fluorine atom in its main chainand side chain include ester compounds formed from α-fluoroacrylic acid,β-fluoroacrylic acid, α,β-fluoroacrylic acid, α-trifluoromethyl acrylicacid, β-trifluoromethyl acrylic acid, α,β-trifluoromethylacrylic acid orthe like with a fluoroalkyl alcohol and/or a derivative thereof,compounds derived by substituting hydrogen of one or more types of vinylmoieties by a fluorine atom or a trifluoromethyl group and substitutinga side chain of the compound with a fluorine atom, a fluoroalkyl groupand/or a derived group therefrom; alicyclic olefin compounds derived bysubstituting hydrogen(s) bonded to one or more types of double bonds bya fluorine atom or a trifluoromethyl group, etc., and having afluorinated alkyl group and/or a derived group therefrom as a sidechain; and the like. The alicyclic olefin compound as referred to hereinmeans a compound that includes a double bond in a part of its ring.

In the fluorine atom-containing polymer, a structural unit that impartsa fluorine atom is not particularly limited, and a structural unitrepresented by the following formula (F1) (hereinafter, may be alsoreferred to as “structural unit (F-I)”) is preferably used as a fluorineatom-imparting structural unit.

In the above formula (F1), R³ represents a hydrogen atom, a fluorineatom, a methyl group or a trifluoromethyl group; A represents a singlebond or a divalent linking group; R⁴ represents linear or branched alkylgroup having 1 to 6 carbon atoms and having at least one fluorine atom,or a monovalent alicyclic hydrocarbon group having 4 to 20 carbon atomsor a derived group therefrom.

“A” in the above formula (F1) represents a divalent linking group, andis exemplified by an oxygen atom, a sulfur atom, a carbonyloxy group, anoxycarbonyl group, an amide group, a sulfonylamide group, a urethanegroup, and the like.

Examples of preferred monomer that gives the structural unit (F-I)include trifluoromethyl(meth)acrylic acid ester,2,2,2-trifluoroethyl(meth)acrylic acid ester,perfluoroethyl(meth)acrylic acid ester, perfluoro-n-propyl(meth)acrylicacid ester, perfluoro-i-propyl(meth)acrylic acid ester,perfluoro-n-butyl(meth)acrylic acid ester,perfluoro-i-butyl(meth)acrylic acid ester,perfluoro-t-butyl(meth)acrylic acid ester,2-(1,1,1,3,3,3-hexafluoropropyl)(meth)acrylic acid ester,1-(2,2,3,3,4,4,5,5-octafluoropentyl)(meth)acrylic acid ester,perfluorocyclohexylmethyl(meth)acrylic acid ester,1-(2,2,3,3,3-pentafluoropropyl)(meth)acrylic acid ester,1-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)(meth)acrylicacid ester, and1-(5-trifluoromethyl-3,3,4,4,5,6,6,6-octafluorohexyl)(meth)acrylic acidester.

In the fluorine atom-containing polymer, the content of the structuralunit (F-I) is typically no less than 5 mol %, preferably no less than 10mol %, and more preferably no less than 15 mol %. When the content ofthe structural unit (F-I) is less than 5 mol %, attaining the recedingcontact angle of no less than 70° may fail, or elution of the acidgenerating agent, etc., from the resist film may not be inhibited. Thefluorine atom-containing polymer may contain only one type, or two ormore types of the structural unit (F-I).

In addition to the structural unit that includes a fluorine atom in itsstructure, the fluorine atom-containing polymer may include at least onetype of “other structural units” such as, for example: in order tocontrol rates of dissolution in developer solutions, a structural unithaving an acid-labile group, as well as a structural unit having alactone skeleton, a hydroxyl group, a carboxyl group and/or the like, ora structural unit having an alicyclic group; and/or a structural unitderived from an aromatic compound for inhibiting scattering byreflection of light from the substrate.

The structural unit having an acid-labile group is exemplified by astructural unit represented by the following formula (F2) (hereinafter,may be also referred to as “structural unit (F-II)”).

In the formula (F2), R⁵ represents a hydrogen atom, a fluorine atom, amethyl group or a trifluoromethyl group; and R⁶ to R⁸ each independentlyrepresent a monovalent alicyclic hydrocarbon group having 4 to 20 carbonatoms or a derived group therefrom, or a linear or branched alkyl grouphaving 1 to 4 carbon atoms.

The monovalent alicyclic hydrocarbon group having 4 to 20 carbon atomsrepresented by R⁵ in the above formula (F2) is exemplified by a groupderived from an alicyclic ring of a cycloalkane such as norbornane,tricyclodecane, tetracyclododecane, adamantane, cyclobutane,cyclopentane, cyclohexane, cycloheptane or cyclooctane; a group obtainedby substituting a part or all of hydrogen atoms of the group derivedfrom the alicyclic ring by, for example, at least one type or at leastone of linear or branched alkyl groups having 1 to 4 carbon atoms suchas a methyl group, an ethyl group, a n-propyl group, an i-propyl group,a n-butyl group, a 2-methylpropyl group, a 1-methylpropyl group and at-butyl group, and cycloalkyl groups having 3 to 10 carbon atoms such asa cyclobutyl group and a cyclohexyl group, and the like. Alternatively,any two of R⁶ to R⁸ may taken together represent a divalent alicyclichydrocarbon group or a derived group therefrom together with the carbonatom to which the two of R⁶ to R⁸ bond. Of these alicyclic hydrocarbongroups, groups derived from an alicyclic ring of norbornane,tricyclodecane, tetracyclododecane, adamantane, cyclopentane orcyclohexane, and groups obtained by substituting hydrogen atoms of thegroup derived from these alicyclic rings by the alkyl group arepreferred.

In addition, examples of the linear or branched alkyl group having 1 to4 carbon atoms represented by R⁶ to R⁸ in the above formula (F2) includea methyl group, an ethyl group, a n-propyl group, an i-propyl group, an-butyl group, a 2-methylpropyl group, a 1-methylpropyl group, a t-butylgroup, and the like.

In the above formula (F2), examples of preferred acid-labile group,i.e., groups that bind to an oxygen atom of an ester group includegroups derived by substituting a t-butyl group, a1-n-(1-ethyl-1-methylpropyl group, a 1-n-(1,1-dimethyl)propyl group, a1-n-(1,1-dimethyl)butyl group, a 1-n-(1,1-dimethyl)pentyl group, a1-(1,1-diethyl)propyl group, a 1-n-(1,1-diethyl)butyl group, a1-n-(1,1-diethyl)pentyl group, a 1-(1-methyl)cyclopentyl group, a1-(1-ethyl)cyclopentyl group, a 1-(1-n-propyl)cyclopentyl group, a1-(1-i-propyl)cyclopentyl group, a 1-(1-methyl)cyclohexyl group, a1-(1-ethyl)cyclohexyl group, a 1-(1-n-propyl)cyclohexyl group, a1-(1-i-propyl)cyclohexyl group, a 1-{1-methyl-1-(2-norbornyl)}ethylgroup, a 1-{1-methyl-1-(2-tetracyclodecanyl)}ethyl group, a1-{1-methyl-1-(1-adamantyl)}ethyl group, a 2-(2-methyl)norbornyl group,a 2-(2-ethyl)norbornyl group, a 2-(2-n-propyl)norbornyl group, a2-(2-i-propyl)norbornyl group, a 2-(2-methyl)tetracyclodecanyl group, a2-(2-ethyl)tetracyclodecanyl group, a 2-(2-n-propyl)tetracyclodecanylgroup, a 2-(2-i-propyl)tetracyclodecanyl group, a 1-(1-methyl)adamantylgroup, a 1-(1-ethyl)adamantyl group, a 1-(1-n-propyl)adamantyl group, a1-(1-i-propyl)adamantyl group, or a group constituted with any of thesealicyclic rings with, for example, at least one type or at least one ofcyclic alkyl groups having 3 to 10 carbon atoms, or linear or branchedalkyl groups having 1 to 4 carbon atoms such as a methyl group, an ethylgroup, a n-propyl group, an i-propyl group, a n-butyl group, a2-methylpropyl group, a 1-methylpropyl group and a t-butyl group, andthe like.

Examples of preferred monomer that gives the structural unit (F-II)include (meth)acrylic acid 2-methyladamantyl-2-yl ester, (meth)acrylicacid 2-methyl-3-hydroxyadamantyl-2-yl ester, (meth)acrylic acid2-ethyladamantyl-2-yl ester, (meth)acrylic acid2-ethyl-3-hydroxyadamantyl-2-yl ester, (meth)acrylic acid2-n-propyladamantyl-2-yl ester, (meth)acrylic acid2-isopropyladamantyl-2-yl ester, (meth)acrylicacid-2-methylbicyclo[2.2.1]hept-2-yl ester, (meth)acrylicacid-2-ethylbicyclo[2.2.1]hept-2-yl ester, (meth)acrylicacid-8-methyltricyclo[5.2.1.0^(2,6)]decan-8-yl ester, (meth)acrylicacid-8-ethyltricyclo[5.2.1.0^(2,6)]decan-8-yl ester, (meth)acrylicacid-4-methyltetracyclo[6.2.1^(3,6.)0^(2,7)]dodecan-4-yl ester,(meth)acrylic acid-4-ethyltetracyclo[6.2.1^(3,6.)02,7]dodecan-4-ylester, (meth)acrylic acid 1-(bicyclo[2.2.1]hept-2-yl)-1-methylethylester, (meth)acrylic acid1-(tricyclo[5.2.1.0^(2,6)]decan-8-yl)-1-methylethyl ester, (meth)acrylicacid 1-(tetracyclo[6.2.1^(3,6.)0^(2,7)]dodecan-4-yl)-1-methylethylester, (meth)acrylic acid 1-(adamantan-1-yl)-1-methylethyl ester,(meth)acrylic acid 1-(3-hydroxyadamantan-1-yl)-1-methylethyl ester,(meth)acrylic acid 1,1-dicyclohexylethyl ester, (meth)acrylic acid1,1-di(bicyclo[2.2.1]hept-2-yl)ethyl ester, (meth)acrylic acid1,1-di(tricyclo[5.2.1.0^(2,6)]decan-8-yl)ethyl ester, (meth)acrylic acid1,1-di(tetracyclo[6.2.1^(3,6.)0^(2,7)]dodecan-4-yl)ethyl ester,(meth)acrylic acid 1,1-di(adamantan-1-yl)ethyl ester, (meth)acrylic acid1-methyl-1-cyclopentyl ester, (meth)acrylic acid 1-ethyl-1-cyclopentylester, (meth)acrylic acid 1-methyl-1-cyclohexyl ester, (meth)acrylicacid 1-ethyl-1-cyclohexyl ester, and the like.

Of these monomers, (meth)acrylic acid 2-methyladamantyl-2-yl ester,(meth)acrylic acid 2-ethyladamantyl-2-yl ester, (meth)acrylic acid2-methylbicyclo[2.2.1]hept-2-yl ester, (meth)acrylic acid2-ethylbicyclo[2.2.1]hept-2-yl ester, (meth)acrylic acid1-(bicyclo[2.2.1]hept-2-yl)-1-methylethyl ester, (meth)acrylic acid1-(adamantan-1-yl)-1-methylethyl ester, (meth)acrylic acid1-methyl-1-cyclopentyl ester, (meth)acrylic acid 1-ethyl-1-cyclopentylester, (meth)acrylic acid 1-methyl-1-cyclohexyl ester, (meth)acrylicacid 1-ethyl-1-cyclohexyl ester, are preferred.

As the structural unit having a lactone skeleton, a structural unitsimilar to the structural unit (III) of the polymer (A) (hereinafter,may be also referred to as “structural unit (F-III)”) may be used.

The structural unit having an alicyclic group (hereinafter, may be alsoreferred to as “structural unit (F-IV)”) is exemplified by a structuralunit represented by the following formula (F4), and the like.

In the formula (F4), R⁹ represents a hydrogen atom, a fluorine atom, amethyl group, or a trifluoromethyl group; and X represents a monovalentalicyclic hydrocarbon group having 4 to 20 carbon atoms.

The monovalent alicyclic hydrocarbon group having 4 to 20 carbon atomsrepresented by X in the above formula (F4) is exemplified by hydrocarbongroups derived from an alicyclic ring of a cycloalkane such ascyclobutane, cyclopentane, cyclohexane, bicyclo[2.2.1]heptane,bicyclo[2.2.2]octane, tricyclo[5.2.1.02,6]decane,tetracyclo[6.2.1.13,6.02,7]dodecane or tricyclo[3.3.1.13,7]decane. Thesehydrocarbon groups derived from an alicyclic ring derived from acycloalkane may have a substituent, and may be substituted with, forexample, at least one type or at least one of linear or branched alkylgroups having 1 to 4 carbon atoms such as a methyl group, an ethylgroup, a n-propyl group, an i-propyl group, a n-butyl group, a2-methylpropyl group, a 1-methylpropyl group and a t-butyl group, or atleast one type or at least one of cycloalkyl group having 3 to 10 carbonatoms. The substituent is not limited to these alkyl groups andcycloalkyl groups, and the hydrocarbon group may be substituted with ahydroxyl group, a cyano group, a hydroxyalkyl group having 1 to 10carbon atoms, a carboxyl group, or an oxygen atom.

Examples of preferred monomer that gives the structural unit (F-IV)include (meth)acrylic acid-bicyclo[2.2.1]hept-2-yl ester, (meth)acrylicacid-bicyclo[2.2.2]oct-2-yl ester, (meth)acrylicacid-tricyclo[5.2.1.02,6]dec-7-yl ester, (meth)acrylicacid-tetracyclo[6.2.1.13,6.02,7]dodec-9-yl ester, (meth)acrylicacid-tricyclo[3.3.1.13,7]dec-1-yl ester, (meth)acrylicacid-tricyclo[3.3.1.13,7]dec-2-yl ester, and the like.

Also, examples of preferred monomer that generates the structural unitderived from an aromatic compound (hereinafter, may be also referred toas “structural unit (F-V)”) include styrene, α-methylstyrene,2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-methoxystyrene,3-methoxystyrene, 4-methoxystyrene,4-(2-t-butoxycarbonylethyloxy)styrene, 2-hydroxystyrene,3-hydroxystyrene, 4-hydroxystyrene, 2-hydroxy-α-methylstyrene,3-hydroxy-α-methylstyrene, 4-hydroxy-α-methylstyrene,2-methyl-3-hydroxystyrene, 4-methyl-3-hydroxystyrene,5-methyl-3-hydroxystyrene, 2-methyl-4-hydroxystyrene,3-methyl-4-hydroxystyrene, 3,4-dihydroxystyrene,2,4,6-trihydroxystyrene, 4-t-butoxystyrene, 4-t-butoxy-α-methylstyrene,4-(2-ethyl-2-propoxy)styrene, 4-(2-ethyl-2-propoxy)-α-methylstyrene,4-(1-ethoxyethoxy)styrene, 4-(1-ethoxyethoxy)-α-methylstyrene,phenyl(meth)acrylate, benzyl(meth)acrylate, acenaphthylene,5-hydroxyacenaphthylene, 1-vinylnaphthalene, 2-vinylnaphthalene,2-hydroxy-6-vinylnaphthalene, 1-naphthyl(meth)acrylate,2-naphthyl(meth)acrylate, 1-naphthylmethyl(meth)acrylate,1-anthryl(meth)acrylate, 2-anthryl(meth)acrylate,9-anthryl(meth)acrylate, 9-anthrylmethyl(meth)acrylate, 1-vinylpyrene,and the like.

The “other structural unit” included in the fluorine atom-containingpolymer may have only one type, or two or more types of the structuralunit (F-II), the structural unit (F-III), the structural unit (F-IV) andthe structural unit (F-V). In the fluorine atom-containing polymer, thecontent of these other structural units is typically no greater than 80mol %, preferably no greater than 75 mol %, and more preferably nogreater than 70 mol % with respect to the entire structural unitsconstituting the fluorine atom-containing polymer.

Synthesis Method of Fluorine Atom-Containing Polymer

The fluorine atom-containing polymer may be synthesized, for example, bypolymerizing the monomer corresponding to each predetermined structuralunit in an appropriate solvent using a radical polymerization initiator.

Acid Diffusion Controller

The acid diffusion controller exerts the effect of controlling diffusionphenomenon of the acid generated from the acid generator (B) upon theexposure in the resist film, and suppressing unfavorable chemicalreactions in unexposed regions. In addition, storage stability of theresultant radiation-sensitive resin composition is further improved, andresolution of the resist is further improved, while suppressingvariation of line width of the resist pattern caused by variation ofpost-exposure delay (PED) from the exposure until a developmenttreatment, thereby capable of imparting superior process stability to beobtained. It is to be noted that the mode of incorporation of the aciddiffusion controller into the composition may be in a free compound formor in an incorporated form as a part of the polymer, or in both of theseforms.

Examples of the acid diffusion control agent include amine compounds,amide group-containing compounds, urea compounds, nitrogen-containingheterocyclic compounds, and the like.

Examples of the amine compounds include mono(cyclo)alkylamines;di(cyclo)alkylamines; tri(cyclo)alkylamines; substituted alkylaniline orderivatives thereof; ethylenediamine,N,N,N′,N′-tetramethylethylenediamine, tetramethylenediamine,hexamethylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylether, 4,4′-diaminobenzophenone, 4,4′-diaminodiphenylamine,2,2-bis(4-aminophenyl)propane,2-(3-aminophenyl)-2-(4-aminophenyl)propane,2-(4-aminophenyl)-2-(3-hydroxyphenyl)propane,2-(4-aminophenyl)-2-(4-hydroxyphenyl)propane,1,4-bis(1-(4-aminophenyl)-1-methylethyl)benzene,1,3-bis(1-(4-aminophenyl)-1-methylethyl)benzene,bis(2-dimethylaminoethyl) ether, bis(2-diethylaminoethyl)ether,1-(2-hydroxyethyl)-2-imidazolidinone, 2-quinoxalinol,N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine,N,N,N′,N″N″-pentamethyldiethylenetriamine, and the like.

Examples of the amide group-containing compound includeN-t-butoxycarbonyl group-containing amino compounds, formamide,N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide,N,N-dimethylacetamide, propionamide, benzamide, pyrrolidone,N-methylpyrrolidone, N-acetyl-1-adamantylamine,tris(2-hydroxyethyl)isocyanurate, and the like.

Examples of the urea compounds include urea, methylurea,1,1-dimethylurea, 1,3-dimethylurea, 1,1,3,3-tetramethylurea,1,3-diphenylurea, tri-n-butylthiourea, and the like.

Examples of the nitrogen-containing heterocyclic compounds includeimidazoles; pyridines; piperazines; pyrazine, pyrazole, pyridazine,quinoxaline, purine, pyrrolidine, piperidine, piperidine ethanol,3-piperidino-1,2-propanediol, morpholine, 4-methylmorpholine,1-(4-morpholinyl)ethanol, 4-acetylmorpholine,3-(N-morpholino)-1,2-propanediol, 1,4-dimethylpiperazine,1,4-diazabicyclo[2.2.2]octane, and the like.

Also, a photodegradable base which is sensitized upon exposure togenerate a weak acid may be used as the acid diffusion control agent.The photodegradable base generates an acid at light-exposed sites,leading to an increase of insolubility of the polymer (A) in thedeveloper solution, and as a result, roughness of the surface of thelight-exposed sites after development is suppressed. On the other hand,the photodegradable base exerts a high acid-capturing function by ananion at light-unexposed sites and serves as a quencher, and thuscaptures the acid diffused from the light-exposed sites. In other words,since the photodegradable base serves as a quencher only atlight-unexposed sites, the contrast resulting from a deprotectionreaction is improved, and consequently the resolution can be furtherimproved. An exemplary photodegradable base includes onium saltcompounds which degrade upon the exposure and lose their acid diffusioncontrollability. Examples of the onium salt compounds include sulfoniumsalt compounds represented by the following formula (D1), and iodoniumsalt compounds represented by the following formula (D2).

In the above formula (D1) and formula (D2), R¹⁰ to R¹⁴ eachindependently represent a hydrogen atom, an alkyl group, an alkoxygroup, a hydroxyl group, a halogen atom or —SO₂—R^(C), wherein R^(C)represents an alkyl group, a cycloalkyl group, an alkoxy group or arylgroup; Z⁻ represents OH⁻, R¹⁵—COO⁻, R^(D)—SO₂—N⁻—R¹⁵, R¹⁵—SO₃ ⁻ or ananion represented by the following formula (D3), wherein R¹⁵ representsa linear or branched alkyl group having 1 to 10 carbon atoms, acycloalkyl group having 3 to 20 carbon atoms, an aryl group having 6 to30 carbon atoms, or an alkaryl group having 7 to 30 carbon atoms,wherein a part or all of hydrogen atoms of the alkyl group, thecycloalkyl group, the aryl group and the alkaryl group are notsubstituted or substituted, and R^(D) represents a linear or branchedalkyl group having 1 to 10 carbon atoms, or a cycloalkyl group having 3to 20 carbon atoms which may have a substituent, wherein a part or allof hydrogen atoms of the alkyl group and the cycloalkyl group are notsubstituted or substituted by a fluorine atom, and provided that Z⁻represents R¹⁵—SO₃ ⁻, any case where a fluorine atom binds to the carbonatom to which SO₃ ⁻ bond is excluded.

In the above formula (D3), R¹⁶ represents a linear or branched alkylgroup having 1 to 12 carbon atoms, or a linear or branched alkoxyl grouphaving 1 to 12 carbon atoms, wherein a part or all of hydrogen atomsincluded in the above alkyl group and alkoxyl group are not substitutedor substituted by a fluorine atom; and u is an integer of 0 to 2.

The R¹⁰ to R¹⁴ preferably represent a hydrogen atom or —SO₂—R^(C). Also,R^(C) represents preferably a cycloalkyl group, and more preferably acyclohexyl group.

Examples of the alkyl group represented by R¹⁵ include a methyl group,an ethyl group, a propyl group, an i-propyl group, a butyl group, ani-butyl group, a t-butyl group and the like, and groups derived bysubstituting a part or all of hydrogen atoms of these groups, and thelike.

Examples of the cycloalkyl group represented by R¹⁵ include acyclopentyl group, a cyclohexyl group, a norbornyl group, atricyclodecanyl group, a tetracyclododecanyl group, an adamantyl groupand the like, and groups derived by substituting a part or all ofhydrogen atoms of these groups, and the like.

Examples of the aryl group represented by R¹⁵ include a phenyl group, anaphthyl group, an anthryl group and the like, and groups derived bysubstituting a part or all of hydrogen atoms of these groups, and thelike.

Examples of the alkaryl group represented by R¹⁵ include a benzyl group,a phenylethyl group, a phenylpropyl group, and groups derived bysubstituting a part or all of hydrogen atoms of these groups, and thelike.

The substituent which may be included in the alkyl group, the cycloalkylgroup, the aryl group and the alkaryl group is exemplified by a hydroxylgroup, a halogen atom, an alkoxy group, a lactone group, analkylcarbonyl group, and the like.

Examples of the alkyl group represented by R^(D) include a methyl group,an ethyl group, a propyl group, a butyl group, and the like.

Examples of the cycloalkyl group represented by R^(D) include acyclopentyl group, a cyclohexyl group, a norbornyl group, an adamantylgroup, and the like.

The photodegradable base is exemplified by compounds represented by thefollowing formulae, and the like.

The content of the acid diffusion control agent in theradiation-sensitive resin composition is preferably less than 10 partsby mass with respect to 100 parts by mass of the polymer (A). When thetotal amount used exceeds 10 parts by mass, sensitivity as a resisttends to be deteriorated. These acid diffusion control agents may beused either alone, or in combination of two or more thereof.

Solvent

The composition typically contains a solvent. The solvent is notparticularly limited as long as the solvent can at least dissolve thepolymer (A), and the acid generator (B), and optional components addedas required. Examples of the solvent include alcohol solvents, ethersolvents, ketone solvents, amide solvents, ester solvents and mixedsolvents thereof, and the like.

Specific examples of the solvent include similar organic solvents tothose exemplified in connection with the step (3) of forming a pattern.Among these, propylene glycol monomethyl ether acetate, cyclohexanoneand γ-butyrolactone are preferred. These solvents may be used eitheralone, or in combination of two or more thereof.

Surfactant

The surfactant achieves an effect of further improving coating property,striation, developability and the like. Examples of the surfactantinclude nonionic surfactants such as polyoxyethylene lauryl ether,polyoxyethylene stearyl ether, polyoxyethylene oleyl ether,polyoxyethylene n-octylphenyl ether, polyoxyethylene n-nonylphenylether, polyethylene glycol dilaurate, polyethylene glycol distearate,and the like. Commercially available products of the surfactant includeKP341 (Shin-Etsu Chemical Co., Ltd.); POLYFLOW No. 75, and No. 95(Kyoeisha Chemical Co., Ltd.), F-top EF301, EF303, and EF352 (TochemProducts Co. Ltd.), Megafac F171, F173 (Dainippon Ink And Chemicals,Incorporated), Fluorad FC430, and FC431 (Sumitomo 3M Ltd.), AsahiGuardAG710, Surflon S-382, SC-101, SC-102, SC-103, SC-104, SC-105, and SC-106(Asahi Glass Co., Ltd.), and the like. These surfactants may be usedeither alone, or in combination of two or more thereof.

Alicyclic Skeleton-Containing Compound

The alicyclic skeleton-containing compound achieves an effect ofimproving dry etching resistance, pattern configuration, adhesiveness toa substrate, and the like.

Examples of the alicyclic skeleton-containing compound include:

adamantane derivatives such as 1-adamantanecarboxylic acid,2-adamantanone and t-butyl 1-adamantanecarboxylate;

deoxycholic acid esters such as t-butyl deoxycholate,t-butoxycarbonylmethyl deoxycholate and 2-ethoxyethyl deoxycholate;

lithocholic acid esters such as t-butyl lithocholate,t-butoxycarbonylmethyl lithocholate and 2-ethoxyethyl lithocholate;

3-[2-hydroxy-2,2-bis(trifluoromethyl)ethyl]tetracyclo[4.4.0.1^(2,5.)1^(7,10)]dodecane,2-hydroxy-9-methoxycarbonyl-5-oxo-4-oxa-tricyclo[4.2.1.0^(3,7)]nonane,and the like. These alicyclic skeleton-containing compounds may be usedeither alone, or in combination of two or more thereof.

Sensitizing Agent

The sensitizing agent exhibits an action of increasing the amount of theacid generator (B) produced, and thus has an effect of improving“apparent sensitivity” of the radiation-sensitive resin composition.

The sensitizing agent is exemplified by carbazoles, acetophenones,benzophenones, naphthalenes, phenols, biacetyl, eosin, rose bengal,pyrenes, anthracenes, phenothiazines, and the like. These sensitizingagent may be used either alone, or in combination of two or morethereof.

Preparation of Radiation-Sensitive Resin Composition

The radiation-sensitive resin composition can be prepared by mixing, forexample, the polymer (A), the acid generator (B) and the optionalcomponent(s) at a certain ratio. Also, it is possible to prepare theradiation-sensitive resin composition in a state of being dissolved ordispersed in an appropriate organic solvent.

EXAMPLES

Hereinafter, the present invention will be explained more specificallyby way of Examples, but the present invention is not limited to theseExamples. Methods of the determination of various types of physicalproperty values are shown below.

Weight Average Molecular Weight (Mw) and Number Average Molecular Weight(Mn)

The Mw and the Mn of the polymer were determined by gel permeationchromatography (GPC) using GPC columns (“G2000 HXL”×2, “G3000 HXL×1,“G4000 HXL”×1) manufactured by Tosoh Corporation under the followingconditions.

eluent: tetrahydrofuran (manufactured by Wako Pure Chemical Industries,Ltd.)

flow rate: 1.0 mL/min

sample concentration: 1.0% by mass

amount of injected sample: 100 μL

detector: differential refractometer

standard substance: mono-dispersed polystyrene

Content of Low Molecular Weight Component

The content (% by mass) low molecular weight component (component havinga molecular weight of less than 1,000) in the polymer (A) was determinedby high performance liquid chromatography (HPLC) using “Inertsil ODS-25μm column” (4.6 mmφ×250 mm) manufactured by GL Sciences, Inc., under thefollowing conditions.

eluent: acrylonitrile/0.1% aqueous phosphoric acid solution

flow rate: 1.0 mL/min

sample concentration: 1.0% by mass

amount of injected sample: 100 μL

detector: differential refractometer

¹³C-NMR Analysis:

The analysis was carried out using “JNM-EX400” manufactured by JEOL,Ltd., with DMSO-d₆ for use as a solvent for measurement.

Synthesis of Polymer (A)

In each Synthesis Example, polymers (A-1) to (A-13), (a-1) and (a-2),and a fluorine atom-containing polymer (C-1) described later weresynthesized using compounds each represented by the following formulae(M-1) to (M-10) (hereinafter, may be referred to as “compound (M-1)”).

Synthesis Example 1 Synthesis of Polymer (A-1)

A monomer solution was prepared by dissolving 43.08 g (50 mol %) of thecompound (M-1) and 56.92 g (50 mol %) of the compound (M-7) in 200 g of2-butanone, and then adding thereto 4.21 g (5 mol % with respect to thetotal amount of a monomer compounds) of AIBN. A 1,000 mL three-neckedflask charged with 100 g of 2-butanone was purged with nitrogen for 30minutes, and thereafter heated to 80° C. with stirring. The monomersolution prepared was added dropwise using a dropping funnel over 3 hrs.The time when dropwise addition was started was assumed to be a starttime point of the polymerization reaction, and the polymerizationreaction was carried out for 6 hours. After completion of thepolymerization reaction, the polymerization solution was cooled to nogreater than 30° C. by water-cooling. The cooled polymerization solutionwas charged into 2.00 g of methanol, and the white powder precipitatedwas filtered off. Thus resultant white powder was washed twice with 400g of methanol, and thereafter filtered off and dried at 50° C. for 17hrs to obtain a polymer (A-1) in the form of a white powder (73 g;yield: 73%). The Mw of the obtained polymer (A-1) was 7,730, the Mw/Mnwas 1.51, and the content of the low molecular weight component was0.05% by mass. In addition, the contents of structural unit derived fromthe compound (M-1) and the structural unit derived from the compound(M-7) in the polymer (A-1) as determined by the ¹³C-NMR analysis were47.3 mol % and 52.7 mol %, respectively.

Synthesis Examples 2 to 17

Polymers (A-2) to (A-15), and polymers (a-1) and (a-2) were obtained ina similar manner to Synthesis Example 1 except that the type and theamount blended of each monomer compound used, and the charged amount ofAIBN as a polymerization initiator (molar ratio with respect to thetotal amount of the monomer compounds) were as presented in Tables 1-1and 1-2. Also, the content of the structural units derived from eachmonomer compound, the Mw, the Mw/Mn ratio and the content of the lowmolecular weight component of the obtained each polymer are collectivelyshown in Tables 1-1 and 1-2.

TABLE 1-1 Content of Ratio of charged monomer Amount Content ofstructural units low- structural structural structural of structuralstructural structural molecular (A) unit (I) unit (II) unit (III)charged unit (I) unit (II) unit (III) weight Com- com- mol com- mol com-mol AIBN com- mol com- mol com- mol Mw/ component ponent pound % pound %pound % (mol %) pound % pound % pound % Mw Mn (% by mass) Synthesis A-1M-1 50 — — M-7 50 5.0 M-1 47.3 — — M-7 52.7  7,730 1.51 0.05 Example 1Synthesis A-2 M-1 50 — — M-7 50 2.0 M-1 50.1 — — M-7 49.9 13,020 1.560.04 Example 2 Synthesis A-3 M-1 50 — — M-7 50 1.0 M-1 50.3 — — M-7 49.720,890 1.61 0.03 Example 3 Synthesis A-4 M-2 50 — — M-7 50 1.5 M-2 49.4— — M-7 50.6 16,580 1.59 0.05 Example 4 Synthesis A-5 M-3 50 — — M-7 503.0 M-3 48.1 — — M-7 51.9  9,860 1.48 0.04 Example 5 Synthesis A-6 M-450 — — M-7 50 2.0 M-4 46.9 — — M-7 53.1 13,460 1.53 0.05 Example 6Synthesis A-7 M-1 40 — — M-5 10 3.5 M-1 38.1 — — M-5  9.0  8,790 1.490.05 Example 7 M-7 50 M-7 52.9 Synthesis A-8 M-1 35 — — M-7 50 5.0 M-133.0 — — M-7 54.1  7,020 1.50 0.03 Example 8 M-6 15 M-6 12.9

TABLE 1-2 Content of Ratio of charged monomer Amount Content ofstructural units low- structural structural structural of structuralstructural structural molecular (A) unit (I) unit (II) unit (III)charged unit (I) unit (II) unit (III) weight Com- com- mol com- mol com-mol AIBN com- mol com- mol com- mol Mw/ component ponent pound % pound %pound % (mol %) pound % pound % pound % Mw Mn (% by mass) Synthesis A-9 M-3  40 — — M-7 50 2.0 M-3  38.4 — — M-7 51.4 11,740 1.55 0.04 ExampleM-10 10 M-10 10.2  9 Synthesis A-10 M-1  40 — — M-7 50 2.0 M-1  39.2 — —M-7 53.2 11,910 1.59 0.03 Example M-6  10 M-6   7.6 10 Synthesis A-11M-3  40 — — M-7 50 2.0 M-3  39.7 — — M-7 52.6 11,430 1.53 0.04 ExampleM-6  10 M-6   7.7 11 Synthesis A-12 M-2  45 — — M-7 40 1.5 M-2  43.9 — —M-7 40.8 14,870 1.58 0.04 Example M-10 15 M-10 15.3 12 Synthesis A-13M-3  45 — — M-7 40 2.5 M-3  44.1 — — M-7 40.2 10,260 1.50 0.03 ExampleM-10 15 M-10 15.7 13 Synthesis a-1 M-1  50 — — M-7 50 10.0 M-1  46.2 — —M-7 53.8  4,700 1.41 0.07 Example 14 Synthesis a-2 M-1  30 M-8 20 M-7 504.0 M-1  28.1 M-8 18.8 M-7 53.1  7,840 1.48 0.05 Example 15

(C) Synthesis of Fluorine Atom-Containing Polymer Synthesis Example 18Synthesis of Polymer (C-1)

A monomer solution was prepared by dissolving 71.67 g (70 mol %) of thecompound (M-2) and 28.33 g (30 mol %) of the compound (M-9) in 100 g of2-butanone, and then adding thereto 10.35 g of dimethyl2,2′-azobisisobutyrate. A 1,000 mL three-necked flask charged with 100 gof 2-butanone was purged with nitrogen for 30 minutes, and thereafterheated to 80° C. with stirring. The monomer solution prepared was addeddropwise using a dropping funnel over 3 hrs. The time when dropwiseaddition was started was assumed to be a start time point of thepolymerization reaction, and the polymerization reaction was carried outfor 6 hours. After completion of the polymerization reaction, thepolymerization solution was cooled to no greater than 30° C. bywater-cooling. The reaction solution was transferred to a 4 L separatoryfunnel, then homogenously diluted with 300 g of n-hexane, and 1,200 g ofmethanol was charge thereto followed by mixing. Subsequently, 60 g ofdistilled water was charged, and the mixture was further stirred andallowed to stand for 30 min. Thereafter, the under layer was recoveredto give a propylene glycol monomethyl ether acetate solution (yield:60%). The Mw of the obtained polymer (C-1) was 7,200, the Mw/Mn was2.00, and the content of the low molecular weight component was 0.07% bymass. In addition, the contents of structural unit derived from thecompound (M-2) and the structural unit derived from the compound (M-9)in the polymer (C-1) as determined by the ¹³C-NMR analysis were 71.1 mol% and 28.9 mol %, respectively.

Preparation of Radiation-Sensitive Resin Composition

Each component (acid generating agent (B), acid diffusion control agent(D) and solvent (E)) that constitutes the radiation-sensitive resincompositions in addition to the polymers (A-1) to (A-15), (a-1) and(a-2), and (C-1) prepared in the Examples and Synthesis Examples isshown below.

(B) Acid Generating Agent

Compounds represented by the following formulae (B-1) and (B-2),respectively

-   -   (B-1): triphenylsulfonium        6-adamantylcarbonyloxy-1,1,2,2-tetrafluorohexane-1-sulfonate    -   (B-2): 2-adamantyl-1,1-difluoroethane-1-sulfonate

(D) Acid Diffusion Control Agent

Compounds represented by the following formulae (D-1) to (D-6),respectively

-   -   (D-1): 4-hydroxy-N-amyloxycarbonylpiperidine    -   (D-2): triphenylsulfonium salicylate    -   (D-3): triphenylsulfonium camphorsulfonate    -   (D-4): triphenylsulfonium N-n-butyltrifluoromethylsulfoneamide    -   (D-5): 4-cyclohexylsulfonylphenyldiphenylsulfonium        1,2-di(cyclohexyloxycarbonyl)ethane-1-sulfonate    -   (D-6): 4-cyclohexylsulfonylphenyldiphenylsulfonium        1,2-di(norbornanelactonyloxycarbonyl)ethane-1-sulfonate

(E) Solvent

-   -   (E-1): propylene glycol monomethyl ether acetate    -   (E-2): cyclohexanone    -   (E-3): y-butyrolactone

Example 1

A radiation-sensitive resin composition (J-1) was prepared by mixing 100parts by mass of the polymer (A-1) obtained in Synthesis Example 1, 3parts by mass of the fluorine atom-containing polymer (C-1) obtained inSynthesis Example 11, 11 parts by mass of the acid generating agent(B-1), 4.5 parts by mass of the acid diffusion control agent (D-2), andas the solvent 1,620 parts by mass of (E-1), 700 parts by mass of (E-2)and 30 parts by mass of (E-3), and then filtering the obtained mixturethrough a filter having a pore size of 0.20 μm.

Examples 2 to 19 and Synthesis Example 19 to 21

Each of radiation-sensitive resin compositions (J-2) to (J-21) and (j-1)to (j-3) was prepared in a similar manner to Example 1 except that eachcomponent of the type and the amount blended shown in Tables 2-1 and 2-2below was mixed.

TABLE 2-1 (C) Fluorine (B) Acid atom- (D) Acid (A) generating containingdiffusion Radiation- Component agent polymer control agent (E) Solventsensitive parts parts parts parts parts resin by by by by by compositiontype mass type mass type mass type mass type mass Example 1  J-1 A-1 100B-1 11 C-1 3 D-2 4.5 E-1/E-2/E-3 1,620/700/30 Example 2  J-2 A-1 100 B-28.5 C-1 3 D-1 1 E-1/E-2/E-3 1,620/700/30 Example 3  J-3 A-2 100 B-1 11C-1 3 D-3 5.5 E-1/E-2/E-3 1,620/700/30 Example 4  J-4 A-2 100 B-2 8.5C-1 3 D-2 4.5 E-1/E-2/E-3 1,620/700/30 Example 5  J-5 A-3 100 B-1 11 C-13 D-1 1 E-1/E-2/E-3 1,620/700/30 Example 6  J-6 A-4 100 B-1 11 C-1 3 D-24.5 E-1/E-2/E-3 1,620/700/30 Example 7  J-7 A-5 100 B-2 8.5 C-1 3 D-24.5 E-1/E-2/E-3 1,620/700/30 Example 8  J-8 A-6 100 B-1 11 C-1 3 D-3 4.5E-1/E-2/E-3 1,620/700/30 Example 9  J-9 A-7 100 B-1 11 C-1 3 D-1 1E-1/E-2/E-3 1,620/700/30 Example 10  J-10 A-8 100 B-2 8.5 C-1 3 D-2 4.5E-1/E-2/E-3 1,620/700/30 Example 11  J-11 A-1 100 B-1 11 C-1 3 D-4 5E-1/E-2/E-3 1,620/700/30 Example 12  J-12 A-1 100 B-1 11 C-1 3 D-5 8.5E-1/E-2/E-3 1,620/700/30

TABLE 2-2 (C) Fluorine (B) Acid atom- (D) Acid (A) generating containingdiffusion Radiation- Component agent polymer control agent (E) Solventsensitive parts parts parts parts parts resin by by by by by compositiontype mass type mass type mass type mass type mass Example 13 J-13 A-1 100 B-1 11 C-1 3 D-6 9.5 E-1/E-2/E-3 1,620/700/30 Example 14 J-14 A-5 100 B-2 8.5 C-1 3 D-4 5 E-1/E-2/E-3 1,620/700/30 Example 15 J-15 A-9 100 B-1 11 C-1 3 D-3 5.5 E-1/E-2/E-3 1,620/700/30 Example 16 J-16 A-10100 B-2 8.5 C-1 3 D-2 4.5 E-1/E-2/E-3 1,620/700/30 Example 17 J-17 A-11100 B-2 8.5 C-1 3 D-6 9.5 E-1/E-2/E-3 1,620/700/30 Example 18 J-18 A-12100 B-1 11 C-1 3 D-2 4.5 E-1/E-2/E-3 1,620/700/30 Example 19 J-19 A-13100 B-1 11 C-1 3 D-4 5 E-1/E-2/E-3 1,620/700/30 Synthesis j-1 a-1 100B-1 11 C-1 3 D-2 4.5 E-1/E-2/E-3 1,620/700/30 Example 17 Synthesis j-2a-1 100 B-2 8.5 C-1 3 D-1 1 E-1/E-2/E-3 1,620/700/30 Example 18Synthesis j-3 a-2 100 B-1 11 C-1 3 D-2 4.5 E-1/E-2/E-3 1,620/700/30Example 19

Formation of Resist Pattern Example 22

On a 12-inch silicon wafer which had been provided with an underlayerantireflective film (“ARC66”, manufactured by Nissan ChemicalIndustries, Ltd.) having a film thickness of 105 nm, a coating filmhaving a film thickness of 100 nm was provided using theradiation-sensitive resin composition (J-1) prepared in Example 1, andthen soft baking (SB) was carried out at 90° C. for 60 sec. Next, thecoating film was exposed through a mask pattern by which a patternprovided after reduction projection had a dot of 55 nm and a pitch of110 nm under conditions involving NA of 1.3, iNA of 1.27 and a ratio of0.800, with Quadrupole, using an ArF excimer laser liquid immersionscanner (“NSR S610C”, manufactured by NIKON Corporation). After theexposure, post-exposure baking (PEB) was carried out at 105° C. for 60sec. Subsequently, the film was developed with methyl-n-amyl ketone at23° C. for 30 sec, and subjected to a rinse treatment with4-methyl-2-pentanol for 10 sec and dried to obtain a resist pattern. Inaccordance with this procedure, an exposure dose at which the areathrough a mask pattern that yield a dot of 55 nm and a pitch of 110 nmforms a hole pattern with a diameter of 55 nm was defined as an optimumexposure dose (Eop) (unit: mJ/cm²). It is to be noted that a scanningelectron microscope (“CG-4000”, manufactured by HitachiHigh-Technologies Corporation) was used for line-width measurement.

Examples 23 to 42 and Comparative Examples 1 to 3

Each resist pattern was formed in a similar manner to Example 22 exceptthat the radiation-sensitive resin composition used and the PEBtemperature were as shown in Table 3.

Evaluations

Film loss amount of the resist film was evaluated on a resist filmformed according to the following method. In addition, criticaldimension uniformity (CDU), mask error enhancement factor (MEEF) andresolution were evaluated on the resist pattern obtained in Examples 22to 42 and Comparative Examples 1 to 3 using an ArF excimer laser as alight source. The results of evaluations obtained are shown in Table 3.

Film Loss Amount

First, an 8-inch silicon wafer which had been provided with anunderlayer antireflective film (“ARC29A”, manufactured by BrewerScience, Inc.) having an film thickness of 77 nm, a coating film havingan initial film thickness of 150 nm was provided using each of theradiation-sensitive resin compositions prepared in Examples andComparative Examples, and then soft baking (SB) was carried out at 90°C. for 60 sec. Next, the entire face of the wafer was exposed at theoptimum exposure dose (Eop) that allows a hole pattern having a diameterof 55 nm to be formed, without using a mask under conditions involvingNA of 0.78 and sigma of 0.90, with Conventional, using an ArF excimerlaser scanner (“NSR S306C”, manufactured by NIKON Corporation). Afterthe exposure, PEB was carried out at a temperature shown in Table 3 for60 sec. Subsequently, the film was developed with methyl-n-amyl ketoneat 23° C. for 30 sec, and subjected to a rinse treatment with4-methyl-2-pentanol for 10 sec and dried. The film thickness ofremaining coating films after completion of a series of process wasmeasured, and a value obtained by reducing the remaining film thicknessfrom the initial film thickness was defined as a film loss amount (unit:nm). It is to be noted that the film thickness was measured using anoptical interferometric film thickness measurement system (“Lambda Ace”,manufactured by Dainippon Screen Mfg. Co., Ltd.). With respect to thedetermined film loss amount, evaluation was made as: “favorable” whenthe value was less than 20 nm; and “unfavorable” when the value was noless than 20 nm. The values of the film loss amount obtained are shownin Table 3.

Critical Dimension Uniformity (CDU)

A total of 30 hole patterns having a diameter of 55 nm formed at the Eopas defined above in pattern formation of each of Examples andComparative Examples were subjected to line-width measurement, and anaverage deviation of the measurement values obtained in the line-widthmeasurement of the total of 30 hole patterns was calculated. Thus, CDUwas determined by multiplication of the average deviation by three. Withrespect to the CDU values, evaluation was made as: “favorable” when theCDU value was less than 2.50; “somewhat favorable” when the CDU valuewas no less than 2.50 and less than 3.50; and “unfavorable” when the CDUvalue was no less than 3.50. The values of CDU obtained are shown inTable 3.

Mask Error Enhancement Factor (MEEF)

In a similar manner to pattern formation of each of Examples andComparative Examples, holes were formed through the resist film using aportion of a mask pattern that yield a dot diameter of 51 nm, 53 nm, 55nm, 57 nm or 59 nm of the pattern after reduction projection, at the Eopas defined above. The diameters (nm) were plotted along the ordinatewith respect to the size (nm) of the mask pattern along abscissa. Astraight line was obtained, and the slope of the straight line wasdetermined as MEEF. The MEEF value (slope of the straight line) moreapproximate to 1 indicates more favorable mask reproducibility. Withrespect to the MEEF values, evaluation was made as: “favorable” when theMEEF value was less than 3.50; “somewhat favorable” when the MEEF valuewas no less than 3.50 and less than 4.50; and “unfavorable” when theMEEF value was no less than 4.50. The MEEF values obtained are shown inTable 3.

Resolution

In pattern formation of each of the Examples and Comparative Examples,an exposure was carried out through a mask pattern that yield a patternhaving a dot of 55 nm and a pitch of 110 nm after the reductionprojection at an exposure dose that is no less than the Eop. The minimumdimension of the hole pattern obtained with an increasing of theexposure dose was determined, which was employed for evaluation of theresolution (unit: nm). Evaluation was made as: “favorable” when theminimum dimension was less than 50 nm; and “unfavorable” when theminimum dimension was no less than 50 nm. The resolutions obtained areshown in Table 3.

TABLE 3 Evaluation results Radiation- Film sensitive PEB reduction resintemperature Eop amount Resolution composition (° C.) (mJ/cm²) (nm) CDUMEEF (nm) Example 20 J-1  105 14.0 16 2.3 3.4 43 Example 21 J-2  10518.0 16 2.2 3.8 43 Example 22 J-3  105 13.0 12 1.9 3.2 41 Example 23J-4  105 16.5 13 1.9 3.4 42 Example 24 J-5  105 12.5 11 1.8 3.0 40Example 25 J-6  90 14.0 13 2.0 3.4 41 Example 26 J-7  80 17.0 16 2.1 3.640 Example 27 J-8  105 18.5 10 2.0 2.9 40 Example 28 J-9  105 15.5 142.7 3.3 46 Example 29 J-10 100 18.5 17 2.0 3.9 39 Example 30 J-11 10513.5 16 2.4 3.2 43 Example 31 J-12 105 11.0 17 2.1 3.3 40 Example 32J-13 105 11.5 16 2.1 3.3 41 Example 33 J-14 80 16.0 16 2.2 3.4 40Example 34 J-15 85 12.5 17 2.1 3.1 44 Example 35 J-16 95 18.0 16 2.2 3.642 Example 36 J-17 85 18.0 18 2.1 3.4 43 Example 37 J-18 95 12.6 16 1.93.4 41 Example 38 J-19 85 13.0 17 2.2 3.2 40 Comparative j-1 105 16.0 252.7 4.3 47 Example 1 Comparative j-2 105 20.0 26 2.8 4.6 51 Example 2Comparative j-3 105 16.5 28 3.5 5.1 53 Example 3

As shown in Table 3, according to the resist pattern-forming method ofthe embodiment of the present invention, film loss during patternformation of the resist film was successfully prevented, and formationof a resist pattern being superior in CDU and MEEF was enabled. Inaddition, it was revealed that the radiation-sensitive resin compositionof the embodiment of the present invention achieves sufficientresolution.

According to the resist pattern-forming method of the embodiment of thepresent invention, film loss during pattern formation of the resist filmcan be prevented, and formation of a resist pattern that is superior inCDU and MEEF is enabled. In addition, the radiation-sensitive resincomposition of the embodiment of the present invention also achievessufficient resolution.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. A resist pattern-forming method comprising: coating aradiation-sensitive resin composition on a substrate to provide a resistfilm; exposing the resist film; and developing the exposed resist filmusing a developer solution comprising no less than 80% by mass of anorganic solvent, wherein, the radiation-sensitive resin compositioncomprises: a polymer which has a weight average molecular weight interms of the polystyrene equivalent of greater than 6,000 and comprisesa first structural unit that includes an acid-labile group, and lessthan 5 mol % or 0 mol % of a second structural unit that includes ahydroxyl group; and a radiation-sensitive acid generator.
 2. The resistpattern-forming method according to claim 1, wherein the firststructural unit includes a plurality of kinds of structural units, andat least one of the plurality of kinds of structural units is a thirdstructural unit represented by a formula (1):

wherein, in the formula (1), R represents a hydrogen atom, a fluorineatom, a methyl group or a trifluoromethyl group; and R^(p) represents anacid-labile group represented by a formula (i):

wherein, in the formula (i), R^(p1) to R^(p3) each independentlyrepresent an alkyl group having 1 to 4 carbon atoms or an alicyclichydrocarbon group having 4 to 9 carbon atoms; or two of R^(P1) to R^(P3)taken together represent a divalent alicyclic hydrocarbon group having 4to 9 carbon atoms together with the carbon atom to which the two ofR^(P1) to R^(P3) bond, and R^(P1) to R^(P3) other than the two of R^(P1)to R^(P3) represents an alkyl group having 1 to 4 carbon atoms or analicyclic hydrocarbon group having 4 to 9 carbon atoms; or R^(P1) toR^(P3) taken together represent a divalent alicyclic hydrocarbon grouphaving 4 to 9 carbon atoms together with the carbon atom to which R^(P1)to R^(P3) bond.
 3. The resist pattern-forming method according to claim2, wherein R^(p1), R^(p2) and R^(p3) in the formula (i) eachindependently represent an alkyl group having 1 to 4 carbon atoms; orR^(p1) represents an alkyl group having 1 to 4 carbon atoms, and R^(p2)and R^(p3) taken together represent a divalent alicyclic hydrocarbongroup having 4 to 9 carbon atoms together with the carbon atom to whichR^(p2) and R^(p3) bond.
 4. The resist pattern-forming method accordingto claim 2, wherein the first structural unit included in the polymercomprises no less than 60 mol % and no greater than 95 mol % of thethird structural unit.
 5. The resist pattern-forming method according toclaim 1, wherein the organic solvent is an alcohol solvent, an ethersolvent, a ketone solvent, an amide solvent, an ester solvent, ahydrocarbon solvent or a combination thereof.
 6. A radiation-sensitiveresin composition comprising: a polymer which has a weight averagemolecular weight in terms of the polystyrene equivalent of greater than6,000 and comprises a first structural unit that includes an acid-labilegroup, and less than 5 mol % or 0 mol % of a second structural unit thatincludes a hydroxyl group; and a radiation-sensitive acid generator, theradiation-sensitive resin composition being for use in a resistpattern-forming method comprising: using a developer solution comprisingno less than 80% by mass of an organic solvent.